SERIES

Geology and Wine 13.Geographic InformationSystem Characterization ofFour Appellations in WestTexas, USA

Edward W. Hellman1,2, Elvis A.Takow3, Maria D. Tchakerian3, andRobert N. Coulson3

1Texas A&M UniversityAgriLife Research and Extension Center1102 East FM 1294Lubbock, TX, 79403, USAE-mail: ewhellman@ag.tamu.edu

2Department of Plant and Soil ScienceTexas Tech University

3Knowledge Engineering LaboratoryDepartment of EntomologyTexas A&M UniversityCollege Station, TX 77843 USA

SUMMARYTexas produces approximately 90 000hl of wine annually from more than200 wineries and 1214 ha of vineyards.Eight wine grape production regionsare officially recognized as AmericanViticultural Areas (AVAs) in Texas.Improved understanding of the grow-ing conditions within each AVA facili-tates selection of well-adapted cultivars

that is critical for continued successand expansion of the wine industry. Ageographic information system (GIS)was developed to enable enhancedcharacterization of the climatic, geo-logic and edaphic conditions of TexasAVAs. The GIS contains datasetsdescribing climatic variables, geology,soils, elevation and topography, all ofsignificance to grape production. Thispaper characterizes the four viticulturalareas (AVAs) of west Texas: TexasHigh Plains AVA, Escondido ValleyAVA, Texas Davis Mountains AVA,and Mesilla Valley AVA. Common fea-tures of the four AVAs are relativelyhigh elevation, warm to very warmgrowing-season temperatures, mildwinter temperatures, and low annualprecipitation. Local differences in ele-vation and topography modify climaticconditions among AVAs, providingvariations in growing degree-days andripening-period mean temperaturesthat influence the performance ofgrape cultivars. The Texas High Plainsand Texas Davis Mountains AVAs havethe lowest growing degree-days andcoolest ripening-period mean tempera-tures; Escondido Valley and MesillaValley AVAs are drier and warmer,resulting in fruit ripening earlier thanin the High Plains and Davis Moun-tains AVAs. Variable underlying geolo-gy leads to differing soil types plantedto vineyards in each AVA; predomi-nantly loamy fine sands and fine sandyloam in Texas High Plains, silty clayloam and loam in Escondido Valley,loam and clay loam in Texas DavisMountains, and clay loam and sandyloam in Mesilla Valley. West Texasproduces red wines from CabernetSauvignon and Merlot cultivars, whichare notable for good tannin and excel-lent colour; recent planting trends towarm-climate cultivars, including Tem-

pranillo, Sangiovese, Mourvèdre, andGrenache, are producing blendedwines of great promise. Similarly, asolid reputation for white wines fromChenin blanc and Chardonnay is beingenhanced by increased production ofViognier, Vermentino, and otherwarm-climate varietal wines.

SOMMAIRETexas produit environ 90 000 hec-tolitres de vin par année provenant deplus de 200 établissements vinicoles et1214 ha de vignes. Huit régions deproductions de raisins de cuve sontofficiellement reconnues comme zonesviticoles américaines (AVA) en Texas.Une meilleure compréhension des con-ditions de croissance au sein de cha-cune AVA facilite le choix des variétés,(cultivars) adaptées pour le succès etl’expansion continue de l’industrie viti-cole. Un système d’information géo-graphique (SIG) a été développé pourpermettre la caractérisation amélioréedes conditions climatiques, géologiqueset édaphiques de l’AVA de Texas. LeSIG contient les ensembles de donnéesdécrivant les variables climatiques, lagéologie, les sols, l’altitude, et topogra-phie d’importances pour la productionviticole. Ce document caractérise lesquatre Zones viticoles de l’OuestTexas: Texas High Plains, EscondidoValley, Texas Davis Mountains, etMesilla Valley. Les caractéristiquescommunes entre des quatre AVA sontrelativement haute altitude, trèschaudes températures de saison decroissance, les températures de l’hiverdoux et faibles précipitations annuelles.Les variations locales en altitude ettopographie modifient les conditionsclimatiques entre les zones viticolesaméricaines et entraînent des variationsdes degrés-jour de croissance (GDD)et la température moyenne de mûrisse-

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GEOSCIENCE CANADA Volume 38 Number 1 March 2011 7

ment (RPMT), ce qui exercent uneinfluence sur rendement des cultivarsde raisin. Le Texas High Plains et leTexas Davis Mountains zones viticolesont les GDD les plus bas et uneRPMT froide; le Escondido Valley etMesilla Valley zones viticoles sont plussecs et plus chauds, ce qui entraine lemûrissement de fruit plus tôt que dansle High Plains et Davis MountainsAVAs. Variable géologie sous-jacenteconduit à une variation des types de solplantés aux vignobles dans chaqueAVA ; principalement loam sableux etle loam sablo-argileux dans Texas HighPlains, loam limoneux et loam dansEscondido Valley, loam et loamargileux dans Texas Davis Mountains,et loam argileux et loam sableux dansMesilla Valley. Ouest Texas produitdes vins rouges de Cabernet Sauvignonet le Merlot qui se distinguent par letanin et une couleur excellente, les ten-dances récentes à la plantation de cli-mat chaud cultivars, y compris le Tem-pranillo, le Sangiovese, Mourvèdre, etGrenache, produisent des vinsd’assemblages de grandes promesses.De même, une solide réputation pourles vins blancs de Chenin blanc et leChardonnay est améliorer par l’aug-mentation de la production de Viog-nier, Vermentino, et d’autres vins declimat chaud cépages.

INTRODUCTIONThe American southwest, includingparts of west Texas, represents the ear-liest successful viticulture and oldestcontinuous tradition of winemaking inNorth America (Pinney 1989). Sacra-mental wine was necessary for mission-aries to conduct religious services, andthe remoteness of the unsettled south-west required local wine production.Accordingly, Spanish missionaries inthe seventeenth century brought Vitisvinifera grapevines to plant at missionsthey established in the region. In 1681,Franciscans established a mission atYsleta on the Rio Grande near El Paso(Kingston 1988), within the present-day Mesilla Valley winegrowing appel-lation.

Over the next 200 years, wine-growing in the El Paso area (Fig. 1)expanded beyond the missions, becom-ing the most important revenue-pro-ducing crop in the region by the earlypart of the nineteenth century (Pinney

1989). During this period, El Pasoheld a favourable reputation amongtraders for ‘Pass Wine’ as well as thelocal brandy. Grape cultivation nearlyvanished from the area in the earlytwentieth century owing to a period ofextensive flooding along the RioGrande and the passage of prohibitionin Texas in 1919. Renewed interest inwinegrowing led to the creation, in1985, of the Mesilla Valley AmericanViticultural Area, which lies within ElPaso County, Texas and Doña AnaCounty, New Mexico.

Today, the broad region ofwest Texas is a major contributor tothe Texas wine industry, which pro-duces approximately 90 000 hl annually(MKF Research 2008) from more than200 wineries. Vineyards in west Texasaccount for 66% of the approximately1214 ha of vineyards in the state(National Agricultural Statistics Service2009) and the state’s two largest winer-ies are located in this region. There are

four American Viticultural Areas inwest Texas: Texas High Plains, Escon-dido Valley, Texas Davis Mountains,and Mesilla Valley.

An American Viticultural Area(AVA) is strictly geographically focusedcompared to European wine appella-tions, which often prescribe grape cul-tivars and production practices; it is anofficially recognized “delimited grapegrowing region distinguishable by geographicalfeatures, the boundaries of which have beenrecognized and defined” through a petitionprocess (Code of Federal Regulations(CFR) Title 27, Part 4, Subpart C, Sec-tion 4.25). An AVA designation is onetype of appellation permitted onAmerican wine labels to provide con-sumers with information on the grow-ing locale of grapes used in thelabelled wine. Petitions for new viti-cultural areas are considered forapproval by the Alcohol and TobaccoTax and Trade Bureau, provided thereis evidence that the proposed name of

Figure 1. Locations of the eight American Viticultural Areas (AVAs) in Texas: 1)Mesilla Valley, 2) Texas Davis Mountains, 3) Escondido Valley, 4) Fredericksburg inthe Texas Hill Country, 5) Bell Mountain, 6) Texas High Plains, 7) Texas Hill Coun-try, 8) Texoma. Only the Mesilla Valley (1), Texas Davis Mountains (2), EscondidoValley (3) and Texas High Plains (6) AVAs are discussed in this paper.

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the viticultural area is locally or nation-ally known as referring to the areaspecified; the boundaries are as speci-fied; and the geographical features (cli-mate, soil, elevation, physical features,etc.) distinguish the viticultural featuresof the proposed area from surround-ing areas (CFR Title 27, Part 9, SubpartA).

American wine may belabelled with an approved AVA appella-tion, if no less than 85% of the wine isderived from grapes grown within theAVA and the wine has been fully fin-ished in the State, within which thelabelled AVA is located. Vintage-labelled American wine that also dis-plays the AVA must be at least 95%derived from grapes harvested in thelabelled year. The term ‘estate bottled’may be used on a wine label only if thewine is labelled with an AVA appella-tion of origin and the bottling wineryis i) located in the labelled AVA; ii)grew all of the grapes used to makethe wine on land owned or controlledby the winery within the boundaries ofthe AVA; and iii) crushed the grapes,fermented the resulting must, and fin-ished, aged, and bottled the wine in acontinuous process.

The official description ofAVAs published within the CFR Title27, Part 9, Subpart A, details only theAVA boundaries; it does not providethe descriptions of climate and soilsfrom the original petitions, whichmoreover are often limited in detail.Therefore, a geographic informationsystem (GIS) was developed to charac-terize the climatic, geologic and edaph-ic (soil) conditions of Texas AVAs.GIS is a powerful tool for the spatialanalysis of environmental factors atthe landscape level, and has been pre-viously applied to the analysis of theviticultural potential of the UmpquaValley (Jones et al. 2004) and theRogue Valley (Jones et al. 2006) AVAsin Oregon, and to assess viticulturalperformance in the Okanagan andSimilkameen valleys in British Colum-bia (Bowen et al. 2005). The TexasAVA project developed and utilized aGIS to characterize the eight AVAs inthe State, and produced an interactivewebsite, the Winegrowing Regions ofTexas, for public access to the system[txwineregions.tamu.edu].

COMPONENTS OF GISThe Texas AVA GIS (AVATXIS) wasdeveloped by the authors; constructionof the system is described in detailelsewhere (Takow 2008). The GIS lay-ers, data sources, and their relevance togrape production are summarizedbelow.

Elevation and topographyoften have an important influence ongrape production, albeit indirectlythrough effects on temperature andsolar radiation (Jones and Hellman2003). Absolute elevation above sealevel determines temperature, and rela-tive elevation of a site compared tosurrounding topography influencescold air drainage and temperature vari-ations along a slope. The slope andaspect of a site affect sunlight recep-tion and air drainage. Elevation datawere obtained from the National Ele-vation Dataset [seamless.usgs.gov], aseamless mosaic of the highest-resolu-tion, best quality elevation data avail-able across the United States (UnitedStates Geological Survey 2002). Topo-graphic categorization of the TexasAVAs was carried out using 10 m digi-tal elevation models (DEM) to deter-mine areas of higher elevation and tocalculate hill shade values.

Gladstones (1992) detailed theaspects of climate critical to grape pro-duction in his authoritative book Viti-culture and Environment, in which heemphasized the great influence of tem-perature on grape and wine productionas well as the effects of sunlight, rain-fall, and relative humidity. A commonmeasure of biologically effective tem-peratures for grapes is the heat sum-mation index known as growingdegree-days (GDD). This index wasutilized in California to help categorizeregions of the state as a guide to suit-ability of grape varieties (Winkler et al.1974). Although it has limitations, useof GDD has subsequently become arough guide for global comparisons ofgrowing season temperatures amongviticultural regions, and for selection ofclimate-appropriate grape varieties. Theaverage climatic conditions of a givenregion are considered to be the majordeterminants of the grape varieties andstyles of wine produced therein (Jonesand Hellman 2003).

Climatic data were obtainedfrom Daymet [daymet.org], a climatic

database produced from a model thatgenerates daily surfaces of tempera-ture, precipitation, humidity, and radia-tion over large regions of the UnitedStates (Thornton et al. 1997). Themodel utilizes digital elevation modelsand daily observations from an 18-yeardaily dataset (1980–1997) to produceclimatic variables. This daily dataset oftemperature, precipitation, humidityand radiation has been prepared as acontinuous surface at 1 km resolution.Climatic variables used in the charac-terization of Texas AVAs were: dailymaximum temperature, daily minimumtemperature, daily average temperature,and annual precipitation. GDD wasdetermined by the standard methoddeveloped in California (Winkler et al.1974); 10°C was subtracted from themean daily temperature and the cumu-lative sum through the growing season(April 1st through October 31st) calcu-lated. Ripening-period mean tempera-ture (RPMT) was calculated for themonths in which grapes typically ripen.

The underlying geology of aregion influences vineyards throughthe physical and chemical characteris-tics of surface soils evolved fromweathering of parent rock (Wilson1998; Macqueen and Meinert 2006).Climate and geology interact in soil-forming processes, and geology alsodetermines the topography and land-forms of a region. Geologic data wereobtained from the digital geologic mapdatabase of Texas, which was derivedfrom the 1992 Geologic Map of Texas(Stoeser et al. 2005). The UnitedStates Geological Survey obtained orig-inal clear film positives of the Geolog-ic Map of Texas and photographicallyenlarged them onto Mylar film. Thesefilms were scanned, geo-referenced,digitized, attributed, edge-matched, andcombined into a single statewide data-base.

Worldwide, wine grapes aresuccessfully grown on a wide range ofsoils; there is no single soil type that isideal for grape production. Soil char-acteristics define the baseline of waterand nutrient availability, which togetherapply the greatest initial influence ongrapevine vigour (Jones and Hellman2003). The generally accepted criteriafor vineyard suitability were summa-rized by Nicholas (2004): soil depth ofat least 60 to 100 cm, good internal

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drainage, adequate water infiltrationrate, good water holding capacity, pHbetween 5.0 and 8.5 in the root zone,and the absence of toxic concentra-tions of salts or mineral nutrients suchas boron, aluminum or manganese.

The source of soils data wasthe State Soil Geographic (STATSGO)database, which consists of geo-refer-enced map data and associated tablesof attribute data (Soil ConservationService 1994). Map units in STATSGOare a combination of geographicallyassociated phases of soil series. Theattribute database gives the proportion-ate extent of the component soils andthe soil properties. The characteriza-tion of Texas AVAs utilized the follow-ing soil properties: texture, depth,available water capacity, soil pH, andpermeability. Permeability (saturatedhydraulic conductivity) is a measure ofthe ease of water movement in soil.Soils with permeability within therange of 3.6 to 36 cm/hr are mostfavourable for grape production.

CHARACTERIZATION OF WINE-GROWING REGIONSThe State of Texas has an area of 69561 900 ha, within which a broaddiversity of geology, soils, climate, andecosystems exists (Alvarez 2008). Ele-vation ranges from sea level at theGulf of Mexico to over 2400 m in theGuadalupe Mountains of far westTexas. Climate varies from semitropicalto continental. This diversity is catego-rized into seven physiographicprovinces: Gulf Coastal Plains, GrandPrairie, Edwards Plateau, Central TexasUplift, North-Central Plains, HighPlains, and Basin and Range (Wermund2008). There are four AVAs in westTexas (Fig. 1); Texas High Plains AVAis located in the High Plains physio-graphic province, Escondido ValleyAVA lies within the Edwards Plateau,and the Texas Davis Mountains AVAand the Mesilla Valley AVA are foundwithin the Basin and Range physio-graphic province.

Texas High PlainsTexas High Plains AVA (Fig. 1) wasestablished in 1993 to recognize theunique viticultural characteristics ofthis high-elevation plateau composedof deep alluvial materials. It is the sec-ond largest AVA in Texas, containing

nearly 3.6 million ha in the westernpart of the state, mostly south of thePanhandle region (Table 1). As thename indicates, this AVA lies withinthe High Plains sub-region (alsoknown as the Llano Estacado), whichis part of the southernmost extensionof the vast Great Plains physiographicprovince of the central United States.The western boundary of the TexasHigh Plains AVA is the Texas–NewMexico border, where elevation reach-es its highest point at about 1250 m inthe northwestern part of the AVA.The plateau slopes gently down to thesoutheast where the eastern border ofthe AVA follows the 914 m elevationcontour along the Caprock Escarp-ment, the steep transitional zone sepa-rating the High Plains from the lowerRolling Plains sub-region to the east.

Grapes and wine have beenproduced in this region since the mid-1970s, and vineyards here have becomea major grape supplier to wineriesthroughout Texas. At present, thereare just over 440 hectares of vineyardswithin the AVA, although expansioncontinues in an effort to supply therapid growth of the Texas wine indus-

try. Prominent grape cultivars in theregion are Cabernet Sauvignon,Chardonnay, and Merlot (NationalAgricultural Statistics Service 2009) aswell as Muscat blanc. Recent plantingsdemonstrate increased interest in Tem-pranillo, Viognier, Mourvèdre,Grenache, Vermentino, and other culti-vars anticipated to have good adapta-tion to the region.

ClimateThe climate of the Texas High PlainsAVA is semi-arid, with hot summersand mild winters. Temperatures gener-ally decrease with increasing elevationfrom southeast to northwest (Fig. 2a).Most of the region receives an averageannual precipitation of 43.7 to 52.6cm; the range throughout the AVA is41.4 to 63.7 cm, increasing from westto east (Table 1; Fig. 2b). CumulativeGDD (Fig. 2c) follows the pattern ofelevation: the lowest GDD is in thenorthwestern corner of the AVA, aver-aging 2028, and the highest in thesoutheastern region, at 2653. Forcomparison, the low range of degree-days is comparable to the SierraFoothills region of California and the

AmericanViticultural Area

Latitudeb

Longitudeb

Area (ha)

Low High Low High Low High Low HighElevation (m) 914 1274 772 977 1125 2546 1134 1303Climatec

AnnualPrecipitation (cm) 41.4 63.7 34.1 38.5 36.7 49.6 20.4 29.3

Cumulative Growing Degree-

Days (oC)2028 2653 2768 3035 1430 2672 2480 2849

July (oC) - - 26.8 28.4 - - 26.7 28.1 August (oC) 23.8 26.7 26.3 27.8 18.8 25.6 25.5 26.8 Sept. (oC) 19.9 22.6 - - 16.7 22.6 - - January Min.(oC) -5.6 -2.2 -0.8 -0.4 -3.6 -1.5 -2.1 -1.6 Frost Dayse (no.) March - - 3.3 4.3 - - 4.1 6 April 1 6.3 0.3 0.8 1.2 7.2 0.7 1.1aTexas portion of the multi-state Mesilla Valley AVA.

Ripening Period Mean Temp.d

eFrost-sensitive stage of budburst generally occurs before April 1 in Escondido Valley and Mesilla Valley; approximately April 1 or later in Texas High Plains and Texas Davis Mountains.

dRipening period is considered to be the 4 weeks prior to harvest; July and August for Escondido Valley and Mesilla Valley, August and September for Texas High Plains and Texas Davis Mountains.

cSource: Daymet. All data are means for designated period, using digital elevation model based on daily observations and 18 years of data from 1980-1997.

bApproximate coordinates of AVA centroid in decimal degrees.

30.68 N-104.02 W127 578

31.90 N-106.59 W

16 247

33.84 N-102.20 W3 585 048

30.85 N-102.46 W

12 616Range within AVA Range within AVA Range within AVA Range within AVA

Table 1. Geographic coordinates, area, elevation, and climatic variable ranges for the four American Viticultural Areas of west Texas.

Texas High Plains Escondido Valley Texas Davis Mountains Mesilla Valleya

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high range to Fresno, California (Table2). It is noteworthy that the broadrange of degree-days within the TexasHigh Plains AVA overlaps with thedegree-days range of many well-estab-lished wine regions in California,including Napa Valley, Lodi, Paso Rob-les, and Temecula Valley (Jones et al.2010). Grape RPMT ranges from 23.8to 26.7°C in August and 19.9 to 22.6°Cin September (Table 1; Fig. 2d). Nighttime minimum temperatures rangefrom 16.7 to 19.4°C in August andfrom 12.2 to 15.6°C in September.Average daily temperature in January,the coldest month, ranges from 2.1 to5.4°C, and minimum temperatures are-5.6 to -2.2°C. Freeze injury tograpevines occurs sporadically, usuallyin association with a rapid drop in tem-perature while vines are in early stagesof cold acclimation in late autumn orde-acclimation in late winter. Theregion experiences 1 to 6 days of frostin April, presenting a risk of frostdamage, particularly to grape cultivarswith early budburst.

GeologyThe Texas High Plains AVA is under-lain by the Blackwater Draw Formation

(Fig. 3a), a sheet ofQuaternary eoliansediment that is up to 27 m thick (Hol-liday 1989). These sediments vary intexture from sandy in the southwest tosilty and clayey in the northeast; thetextural fining is apparently the resultof downwind sorting. The formationcomprises up to six well-developedburied soils, indicating episodic sedi-mentation, that are similar to theregional surface soils. There are twonarrow west–east trending fields ofeolian sand dunes overlying the forma-tion, and much of the southern regionof the AVA is generally overlaid withupper Quaternary sand sheet deposits(Holliday 2001). The Ogallala Forma-tion, of Miocene to Pliocene age,underlies the Blackwater Draw Forma-tion and consists of sediments (sand,silt, clay, gravel, carbonate) derivedfrom eolian and fluvial deposits. Thisformation is host to the importantOgallala Aquifer, the primary sourcefor agricultural irrigation and drinkingwater in the region.

SoilsThe region is characterized by verydeep (>152 cm), well-developed soils

with accumulations of calcium carbon-ate in the subsoil and clay increasingwith depth. Distribution of generalsoil types in the region correspondsclosely to geology, with texture becom-ing increasing finer from southwest tonortheast (Fig. 3b). The Texas HighPlains AVA contains 31 soil associa-tions, five of which constitute 75% ofthe area: Pullman–Randall–Lofton22.8%, Amarillo–Acuff–Olton 19.5%,Patricia–Amarillo–Gomez 15.5%,Olton–Acuff–Amarillo 9.5%, and Pull-man–Olton–Randall 7.7% (Table 3).Pullman–Randall–Lofton soils haveclayey subsoil horizons with shrink-swell potential and are not commonlyplanted to grapes (Fig. 3b).

The Amarillo–Acuff–Oltonsoil association covers almost 700 000ha (Table 3), primarily in the west-cen-tral part of the AVA (Fig. 3b). It com-prises deep soils with sandy loam tex-ture from 0 to 30 cm depth, transition-ing into sandy clay loam from 30 to200 cm. Permeability of the upper 30cm averages about 8.5 cm/hr; withinthe underlying sandy clay loam it isapproximately 3.2 cm/hr. Soil pH

Figure 2. Spatial distribution of a) elevation, b) annual pre-cipitation, c) cumulative growing degree-days, and d) meanAugust temperature in the Texas High Plains AVA.

Figure 3. Spatial distribution of a) rock types and b) soilassociations in the Texas High Plains AVA.

GEOSCIENCE CANADA Volume 38 Number 1 March 2011 11

increases with depth, from approxi-mately 7.3 in sandy loam to 7.9 to 8.1in sandy clay loam. Available watercapacity ranges from 15 to 28 cm,increasing with depth (Table 3).

The Patricia–Amarillo–Gomezsoil association predominates in thesouthern part of the AVA (Fig. 3b).These soils have a sand texture from 0to 40 cm depth and sandy clay loamfrom 40 to 200 cm (Table 3). Perme-ability within the sand is high (21 to 24cm/hr), decreasing to 3.5 to 6.5 cm/hrin the sandy clay loam. The pH rangesfrom 7.2 to 7.8, and available watercapacity ranges from 12 to 26 cm, bothincreasing with depth.

Vineyards in the Texas HighPlains AVA are predominantly plantedon deep, reddish-brown Patricia andAmarillo loamy fine sands (205.9 ha)and Amarillo fine sandy loam (115.3ha) soils (Fig. 4). The Amarillo andPatricia series are classified taxonomi-cally as fine-loamy, mixed, superactive,thermic Aridic Paleustolls, and arefavoured for their depth and combina-tion of good internal drainage andsubsoil with enough clay for adequatewater-holding capacity (Table 4). Bothsoils are characterized by a friable cal-careous zone in the subsoil; depth tothis zone for Patricia soils is typically152 to 203 cm (Natural ResourcesConservation Service 1999), whereas inAmarillo soils it is 76 to 150 cm (Nat-ural Resources Conservation Service2010). Figure 5 illustrates a typical soilprofile of an Amarillo fine sandy loamhaving an apparent calcareous zone at100 to 140 cm depth. Favourable soil-water characteristics, low annual rainfall(see above), and low to moderate fertil-ity of these soils enables viticulturiststo manage grapevine vigour throughirrigation practices, which is an impor-tant tool in optimizing canopy micro-climate for fruit quality.

Grape and Wine ProductionThe Texas High Plains AVA is home toapproximately 60 vineyards totalling440 ha, and six wineries, including thesecond-largest producer in the state,the Llano Estacado Winery. Vineyardstend to be relatively large (>9 ha),mechanized (Fig. 6), and not associatedwith a winery; grapes are sold to winer-ies both within and external to theTexas High Plains AVA. The region

Table 2. Growing Degree Days for representative viticultural regions of the worldand west Texas AVAs: Texas High Plains, Texas Davis Mountains, Mesilla Valley,and Escondido Valley.

Growing DegreeWinegrowing Region Days (°C)

Barossa Valley, Australia 1848a

Napa Valley, California 1883a

Paso Robles, California 1903a

La Mancha, Spain 1912a

Texas High Plains AVA (low) 2028Sierra Foothills, California 2098a

Clarksburg, California 2176a

Texas Davis Mountains AVA 2190c

Lodi, California 2211a

Temecula Valley, California 2264a

Hunter Valley, Australia 2340b

Jerez-Xéres-Sherry, Spain 2343a

Madera, California 2511a

Fresno, California 2590b

Texas High Plains AVA (high) 2653Mesilla Valley AVA, Texas 2830c

Algiers, Algeria 2880b

Escondido Valley AVA, Texas 2970c

a AVA or designated growing region median value; Jones et al. 2010.b Meinert and Busacca 2000.c Approximate value corresponding to vineyard locations within AVA.

Table 3. Characteristics of predominant soil associations in the Texas High PlainsAmerican Viticultural Area.

Pullman─ Amarillo─ Patricia─ Olton─ Pullman─Predominant Randall─ Acuff─ Amarillo─ Acuff─ Olton─Associationsa Lofton Olton Gomez Amarillo Randall

Area (hectares) 818 986 698 811 557 989 341 293 276 502Depth to bedrock (cm) 152b 152b 152b 152b 152b

Texture Class –upperc clay loam sandy loam sand (40) clay loam clay loam(depth, cm) (10) (30) (20)

Texture Classes –lowerd clay, clay sandy clay sandy clay clay loam clay, clayloam loam loam loam

Permeability 0.92 8.48 23.30 3.44 1.35– upperc (cm/hr)

Permeability 0.34 3.16 4.17 1.65 0.56– lowerd (cm/hr)

pH – upperc 7.1 7.3 7.3 7.3 7.2pH – lowerd 7.7 8.0 7.7 7.8 7.8Available Water Capacity 18 15 12 17 18

(cm) 0-100 cm depthAvailable Water Capacity 26 22 19 24 26

(cm) 100-150 cm depthAvailable Water Capacity 32 28 26 31 32

(cm) 150-250 cm deptha Source: Soil Information for Environmental Modeling and Ecosystem Management,

http://www.soilinfo.psu.edu, utilizing the CONUS-SOIL dataset based on the USDAState Soil Geographic Database (STATSGO).

b Values of 152 cm indicate that bedrock was not encountered within this distance of thesurface; actual depth to bedrock is undetermined.

c Depth from surface of upper soil layers having a uniform texture class; within a soil asso-ciation, permeability and pH values correspond to the same depth.

d Lower soil layers begin with the uppermost layer of a different texture class than theupper layers and extend to the full depth of the soil association.

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first established its winegrowing repu-tation with Cabernet Sauvignon andMerlot, frequently producing medal-winning wines that were commonlyvineyard-designated on the label inrecognition of local terroir. Recentplanting trends have increased produc-tion of grape cultivars common towarm and hot climates, including San-giovese, Vermentino and Tempranillo,and the Rhone cultivars Viognier,Grenache, Mourvèdre, and Syrah. Thehigh quality of varietal wines orRhone-type blends of these cultivars

suggests that theregion may be bet-ter suited to suchwarm-climate cultivars.

Climatic and edaphic condi-tions of the Texas High Plains AVAare conducive to high-quality grapeproduction; although the region is con-sidered to have a hot climate based onGDD, temperatures becomefavourably moderate at night duringthe fruit ripening period because ofthe high elevation and low relativehumidity. Good tannin and colour

development is characteristic of fruitfrom the region and vine fruitfulness ishigh, which are attributable to abun-dant sunlight and possibly an enhancedratio of red to far red light wave-lengths reflected from red soils (Glad-stones 1992). Relatively low annualprecipitation enables grapevine vigourmanagement through irrigation prac-tices. Low rainfall and low relativehumidity also provide an environmentconducive to few fungal diseases ofgrapes.

Escondido ValleyThe Escondido Valley viticultural area,located in Pecos County, Texas (Fig. 1),was established in 1992. This AVA cov-ers approximately 12 600 ha at thenorthern edge of the Stockton Plateau,a western sub-region of the EdwardsPlateau physiographic province imme-diately south of the High Plains. Thesouthern boundary of the AVA isdefined by the 914 m elevation contourline, and Interstate Highway 10 is thenorthern limit. The Escondido ValleyAVA is a mesa-like plateau havingmore topographical variation than theTexas High Plains AVA, althoughmuch of the area is 300 m lower in ele-vation. The landscape is distinguishedby higher elevations in the south andgenerally lower elevation in the northand northeast, ranging from 772 to 976m, with an isolated peak at about 890m in the far northeast end of theregion. Grape cultivation began in the

Figure 4. Distribution of soil types among vineyards in theTexas High Plains AVA.

Figure 5. Soil profile of Amarillo fine sandy loam at KrickHill Vineyards in the Texas High Plains AVA; depth to cal-careous zone at arrow location is 100 cm.

DrainageSoil Series Taxonomic Class Horizon Texture ClassAcuffa Fine-loamy, mixed, A loam, sandy clay loam Well-Drained

superactive, thermic Bt loam, sandy clay loam,Aridic Paleustolls clay loam

Btk sandy clay loam, clay loam

Amarillob Fine-loamy, mixed, Ap loamy fine sand, fine sandy loam Well-Drainedsuperactive, thermic Bt sandy clay loam, clay loamAridic Paleustolls Upper Btk sandy clay loam, clay loam

Lower Btk sandy clay loam, clay loam

Oltonc Fine, mixed, super- A loam, clay loam Well-Drainedactive, thermic Aridic Bt clay loam, clayPaleustolls Btk clay loam, silty clay loam

Bt (where present) loam, sandy clay loam, clay loam

Patriciad Fine-loamy, mixed, A loamy fine sand, fine sand, Well-Drainedsuperactive, thermic fine sandy loamAridic Paleustolls Bt fine sandy loam, sandy clay loam

Btk fine sandy loam, sandy clay loam

Pullmane Fine, mixed, super- A clay loam, silty clay loam Well-Drainedactive, thermic Torrertic Upper Bt clayPaleustolls Lower Bt silty clay, clay

Btk clay loam, silty clay loamsilty clay, clay

Sources: Natural Resources Conservation Service a2008, b2010, c2007, d1999, e2005

Table 4. Taxonomy and characteristics of predominant soil series planted to vineyards in the Texas High Plains American Viticultural Area.

Range of Characteristics

GEOSCIENCE CANADA Volume 38 Number 1 March 2011 13

1980s and the AVA was created toidentify Texas’ largest estate vineyard(Mesa Vineyards; Fig. 7) and Ste.Genevieve winery. Approximately 288ha of wine grapes are in production;predominant cultivars are Cheninblanc, Chardonnay, Cabernet Sauvi-gnon, and Merlot (National Agricultur-al Statistics Service 2009).

ClimateThe Escondido Valley AVA is thewarmest and second-driest growingregion among west Texas AVAs. Airtemperature, GDD, and precipitationvariability are associated with elevation(Fig. 8a to d). Annual precipitation(Table 1) ranges from 34.1 to 38.5 cm,with greater precipitation occurring athigher elevations along the southernborder (Fig. 8b). Cumulative GDD isvery high, ranging from 2768 at thehigher elevations to 3035 at the lowestelevations in the north (Fig. 8c), andaverage about 2970 at Mesa Vineyards,somewhat warmer than Bakersfield,California (2822 GDD; Winkler et al.1974). However, grapes ripen in Julyand August in the Escondido ValleyAVA, suggesting that comparisons withstandard full-season (April to October)degree-day accumulations may not beappropriate. Grape RPMT averages27.6°C in July and 27.1°C in August(Table 1). Winter temperatures are themildest among west Texas AVAs; Janu-ary minimum temperature averagesabout -0.6°C (Table 1). Spring frost

Figure 6. Machine-harvest of Muscat blanc at Young FamilyVineyards in the Texas High Plains AVA. Soil types are Patri-cia and Amarillo loamy fine sands.

Figure 7. Mesa Vineyards, Escondido Valley AVA. Soil type isthe Reagan–Hodgins association.

Figure 8. Spatial distribution of a) elevation, b) annual precipitation, c) cumulativegrowing degree-days, and d) mean August temperature in the Escondido ValleyAVA. The rectilinear patterns result from the relatively coarse (1 km) resolution ofclimatic data relative to the dimensions (18 x 10 km) of the Escondido Valley AVA.

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frequency averages about 3.8 days inMarch and 0.6 days in April at theintermediate elevations where vine-yards are planted.

GeologyThe Escondido Valley AVA lies withina transition zone between the southernextent of Quaternary, alluvial eoliansand, silt, clay, gravel and carbonatedeposits common to the High Plains,and the western extent of the Creta-ceous Edwards Limestone (Fig. 9a).Quaternary deposits account foralmost 40% of the total area and pre-dominate in the central part of theregion, whereas Edwards Limestoneunderlies a slightly larger proportion(43.6%), associated with higher eleva-tions mainly along the southern andeastern boundaries and with a mesa inthe northeast corner. A prominenteast–west band of Quaternary–Tertiaryalluvial deposits of gravel and con-glomerate fill the lowest elevations (772to 790 m) along the northern boundaryof the AVA, corresponding to the bedof present day Tunas Creek. North ofthis band, there are three occurrencesof Cretaceous deposits (limestone,mudstone, dolomite, and chert) of theFredericksburg Group (Fig. 9a).

SoilsThree soil associations, all of which arecalcareous and alkaline (pH 8.1 to 8.2),characterize the Escondido Valley AVA(Table 5): Ector–Rock outcrop–Dev,Reagan–Hodgins–Iraan, andLozier–Rock outcrop–Upton. Themost suitable vineyard soils are foundwithin the Reagan–Hodgins–Iraanassociation, which occupies 38.5% ofthe AVA, generally overlying the Qua-ternary and Tertiary deposits in thenorth and central areas (Fig. 9a, b).Mesa Vineyards is located within thissoil association, somewhat northeast ofthe AVA centroid (Fig. 10). The Rea-gan–Hodgins–Iraan association com-prises very deep (>152 cm) soils hav-ing silty clay loam texture from 0 to 20cm, and loam texture beneath. Perme-ability is moderately high throughout,ranging from 2.56 to 2.68 cm/hr.Available water capacity is good andincreases with depth as the proportionof clay increases, from 14 cm withinthe top 100 cm to 26 cm at depth(Table 5). Soil pH is high (8.1), requir-

ing vineyard management practices toavoid iron and zinc deficiency ingrapevines.

The Ector–Rock outcrop–Devsoil association predominates, underly-ing 58% of the total area, and is gener-ally associated with Edwards Lime-stone geology and the higher elevationsof the southern and eastern portions

of the AVA (Fig. 9b). Because thisassociation is mostly shallow gravelyloam and rock outcrop, it has inade-quate depth for grape production andvery low available water capacity, and istherefore not suitable for grape grow-ing. A small area (3.5%) along thenorthern border of the AVA containsthe Lozier–Rock outcrop–Upton soil

Figure 9. Spatial distribution of a) rock types and b) soil associations in theEscondido Valley AVA.

Predominant AssociationsaEctor

Rock outcropDev

ReaganHodgins

Iraan

Lozier Rockoutcrop

UptonArea (hectares) 7254 4823 451Depth to bedrock (cm) 40 152b 50

Texture Class– upperc (depth, cm) loam (20) silty clay loam (20)

loam (20)

Texture Classes – lowerd other loam other

Permeability – upperc (cm/hr) 10.56 2.68 8.53

Permeability – lowerd (cm/hr) 10.19 2.56 8.05

pH – upperc 8.1 8.1 8.2

pH – lowerd 8.2 8.1 8.2Available Water Capacity (cm) 0-100 cm depth 2 14 3Available Water Capacity (cm)100-150 cm depth - 21 -Available Water Capacity (cm)150-250 cm depth - 26 -

aSource: Soil Information for Environmental Modeling and Ecosystem Management, http://www.soilinfo.psu.edu, utilizing the CONUS-SOIL dataset based on the USDA State Soil Geographic Database (STATSGO).

cDepth from surface of upper soil layers having a uniform texture class; within a soil association, permeability and pH values correspond to the same depth.dLower soil layers begin with the uppermost layer of a different texture class than the upper layers and extend to the full depth of the soil association.

Table 5. Characteristics of predominant soil associations in the Escondido Valley American Viticultural Area.

bValues of 152 cm indicate that bedrock was not encountered within this distance of the surface; actual depth to bedrock is undetermined.

GEOSCIENCE CANADA Volume 38 Number 1 March 2011 15

association (Fig. 9b); these soils aredeveloped on Fredericksburg Groupsubstrate, and have characteristics verysimilar to the Ector–Rockoutcrop–Dev soil association. Thesoils are gravely loams too shallow forgrape production, and have low avail-able water capacity.

Grape and Wine ProductionAs noted above, Ste. Genevieve isTexas’ largest wine producer (58 000hL annually) and is located, along withthe 288 ha Mesa Vineyards, within theEscondido Valley AVA (Figs. 7 and 10).Unlike other Texas wineries, Ste.Genevieve has no tasting room andwine is sold only through distributionto retailers, almost all within Texas.The winery began operation in 1987,producing Cabernet Sauvignon, Mer-lot, Zinfandel, and other red wines, buthas been more recognized for Sauvi-gnon blanc, Chenin blanc, andChardonnay. The hot, dry climateseems particularly favourable for thesewhite wine cultivars. With the abun-dant sunlight and high temperatures inthis AVA, fruit readily attains highsugar content. The long growing sea-son begins in March, earlier in Escon-dido than the other west Texas AVAs,and presents a risk of frost injury tograpevines after budburst. High GDDleads to early ripening, and harvestoccurs in July and August.

Texas Davis MountainsAbout 150 km west of the EscondidoValley AVA (Fig. 1), the Davis Moun-tains rise abruptly from the rockyplains of the Chihuahua Desert withinthe Basin and Range physiographicprovince of far west Texas. The higherelevation of the Davis Mountains cre-ates a unique environment by forcingwesterly winds to rise and cool, con-densing moisture and causing increasedrainfall compared to the surroundingdesert. The Texas Davis MountainsAVA was established in 1998 toacknowledge the distinctive features ofthis AVA, the highest-elevation winegrowing region in Texas. The bound-aries of this AVA encompass much ofthis isolated mountain range, but vine-yards are located at lower elevations(1500 to 1600 m) along the southeast-ern border where favourable soils andirrigation water are available. The pre-

dominant grape varieties grown in thisregion are Cabernet Sauvignon, Sauvi-gnon blanc, Merlot, and Chenin blanc.

ClimateThe varied elevation (1125 to 2546 m;Fig. 11a) and topography of the TexasDavis Mountains creates the broadestrange of climatic variables of all AVAsin west Texas (Table 1). Precipitationis greatest at the highest elevations,which receive almost 50 cm annually(Fig. 11b); vineyards are at elevationsof 1500 to 1600 m, and average 42 to43 cm annual precipitation. Higherelevations experience only 1430 GDDcompared to 2672 at low elevation(Fig. 11c). Favourable vineyard loca-tions in the southeast have approxi-mately 2190 GDD, comparable to thewest central area of the Texas HighPlains AVA and Lodi, California (Table2). Temperatures during fruit ripeningare the lowest among Texas AVAs, andexhibit a similarly broad range associat-ed with elevation (Fig. 11d); RPMTranges from 18.8 to 25.6°C in Augustand 16.7 to 22.6°C in September. Riskof mid-winter freeze injury tograpevines is low, as January minimumtemperatures average about -2°C atvineyard locations. The number offrost days is also associated with eleva-tion, ranging from 1.2 to 7.2 days inApril. Vineyards are at elevations thatexperience frost on average about 2.4days in April, but strategic location ofvineyard sites on slopes can mitigatethe risk of frost injury.

GeologyThe Davis Mountains were formed byvolcanic activity approximately 37 mil-lion years ago (Swanson 1995). MountLivermore is the highest peak at 2555m. The geology of the Texas DavisMountains AVA is dominated by alarge area of older volcanic rocks (rhy-olite, trachyte, lava flows) at lower ele-vations in the north and east, andyounger volcanic rocks (trachyte, rhyo-lite, tuff, latite) at the higher elevationsin the central and southwest areas,including Mount Livermore, BlackMountain and surrounding peaks (Fig.12a). Quaternary alluvium (sand, silt,clay, gravel) and alluvial fan depositsoccur along the southern border, Qua-ternary–Tertiary gravel and conglomer-ate in the northeast corner, and scat-tered areas of Oligocene intrusiverocks (basalt, trachyte, felsic volcanicrock, rhyolite, phonolite) are located inthe west (Fig. 12a).

SoilsThe relatively recent volcanic activity inthis AVA results in a predominance ofrock outcrop, and only a limited areaof soils suitable for vineyards. Thetwo most prevalent soil associations,Rock outcrop–Mainstay–Liv and Brew-ster–Rock outcrop–Liv mostly com-prise non-soil surface bedrock, andtogether constitute 82.5% of the totalarea (Table 6). Both of these associa-tions, as well as the Puerta–Madrone–Rock outcrop association, are consid-ered too shallow (44 to 58 cm to

Figure 10. Satellite imagery of Mesa Vineyards (centre) with overlay of soil associ-ations in the Escondido Valley AVA. This large (288 ha) vineyard lies within theReagan–Hodgins-Iraan soil association displayed in amber.

16

bedrock) for grape production. The Musquiz–Boracho–Santo

Tomas soil association is the mostfavourable in the AVA for grape pro-duction. It underlies 9% of the area,primarily along the southern boundarywhere vineyards have been established,and to a lesser extent along the north-western boundary (Fig. 12b). Soils inthis association are deep (up to 144cm), with loam texture in the upper 20cm, and clay and clay loam at lowerdepths. Permeability is high (4.12cm/hr) in the upper 20 cm, but onlymoderately high (3.07 cm/hr) at depthas clay content increases. Soil pH isfavourable at 7.5 and available watercapacity is good: 12 cm within the top100 cm and 18 cm from 100 to 150 cmdepth.

The Phantom–Rockhouse–Hodgins soil association accounts foronly 1% of the area and is located inthe northeast corner at the lowest ele-vation (1124 to 1300 m) in the AVA.It has a clay loam to loam texture withonly moderately high permeability

(2.84 cm/hr) inthe upper 20 cm, and clay loam belowhaving high permeability (6.25 cm/hr)to a total depth of 142 cm. The pH isfavourable and slightly higher thanMusquiz–Boracho–Santo Tomas, at 7.6to 7.8. Available water capacity is simi-larly favourable at 13 cm within the top100 cm and 20 cm from 100 to 150 cmdepth.

Grape and Wine ProductionThe limited area suitable for vineyardsin the Texas Davis Mountains AVA hasrestricted winery development in theregion. Grapes were first planted in1977 at Blue Mountain Vineyard nearFort Davis; the winery operated from1995 to 2006, producing award-win-ning wines from estate-grown Caber-net Sauvignon and Merlot that werenotable for good colour and tannins.Although there are no operationalwineries in the region today, a vineyardthat cultivates Cabernet Sauvignon andSauvignon blanc provides grapes toPleasant Hill Winery in Brenham,

Texas for appellation-labelled wines.The high-altitude combination

of GDD and relatively cool RPMT ofthe Texas Davis Mountains AVA hasbeen demonstrated to be favourablefor traditional Bordeaux grape culti-vars. Experimentation with warm-cli-mate grape cultivars, as has been donein the Texas High Plains AVA, has notbeen conducted in the region, butresults at the latter AVA suggest similaropportunities for the Texas DavisMountains AVA. Low precipitationreduces the risk of fungal diseases, butrestricts grape production to areas withirrigation wells. Suitable soils in theMusquiz–Boracho–Santo Tomas asso-ciation generally correlate with avail-ability of irrigation water, practicallylimiting grape production to the south-ern border of the AVA. Althoughsuitable vineyard locations are limited,there is potential for additional vine-yard and winery development to takeadvantage of the unique environmentalconditions of this region.

Figure 11. Spatial distribution of a) elevation, b) annual pre-cipitation, c) cumulative growing degree-days, and d) meanAugust temperature in the Texas Davis Mountains AVA. Therectilinear patterns result from the relatively coarse (1 km)resolution of climatic data relative to the dimensions of theTexas Davis Mountains AVA. Figure 12. Spatial distribution of a) rock types, and b) soil

associations in the Texas Davis Mountains AVA.

GEOSCIENCE CANADA Volume 38 Number 1 March 2011 17

Mesilla ValleyThe Mesilla Valley AVA spans twostates, Texas and New Mexico, begin-ning approximately 23 km north ofLas Cruces, New Mexico and extend-ing south along the Rio Grande to ElPaso, Texas (Fig. 1). The Mesilla Valleyis a fertile tableland rising above thefloodplain of the Rio Grande and is animportant irrigated agricultural regionwithin the Chihuahua Desert in theBasin and Range physiographicprovince. This AVA was established in1985 to recognize modern wine grapeproduction within the valley, which isthe location of some of the earliestsuccessful grape growing in the UnitedStates. The appellation generally corre-sponds to the area of its namesake val-ley, trending approximatelynorth–south for 85 km and about 13km east–west; the east and westboundaries are generally defined by the1250 or 1280 m elevation contourlines, but elevations are as high as 1300m in the southeast. The land slopesdown from the eastern and western

boundaries to the Rio Grande, approx-imately in the centre of the valley, at anelevation of about 1150 m.

The total area of the multi-state AVA is 87 340 ha; the Texas por-tion is about 19% (16 247 ha) of thistotal, and occupies the southeasternpart of the entire AVA, north and westof El Paso. It is the westernmost AVAin Texas, approximately 280 km north-west of the Texas Davis Mountains.The predominant grape varieties in thefull AVA are Viognier, Zinfandel, Mus-cat blanc, and Sangiovese. The GISdescriptive analysis focuses only on theTexas portion of the Mesilla ValleyAVA, although conditions are similar inthe remaining area.

ClimateThe Mesilla Valley AVA is by far thedriest in west Texas, with annual pre-cipitation ranging from 20.4 to 29.3 cm(Table 1). Rainfall and other climaticparameters are closely associated withelevation (Fig. 13a); precipitation isleast at the lowest elevations in the

west and increases with elevationtoward the Franklin Mountains in theeast (Fig. 13b). The GDD ranges from2480 to 2849 (Fig. 13c) and averagesabout 2830 in vineyard areas, some-what lower than Escondido Valley andsimilar to Bakersfield, California (2822GDD; Winkler et al. 1974). As in theEscondido Valley, mild winters and awarm growing season lead to earlybudburst and fruit ripening in July andAugust. RPMT is highest in the lowerelevation western part of the region(Fig. 13d), ranging from 26.7 to 28.1°Cin July and 25.5 to 26.8°C in August.January minimum temperatures presentlittle risk of freeze injury to grapevines,averaging about -1.9°C for the AVA.Spring frost days increase with eleva-tion, ranging from 4.1 to 6.0 days inMarch, and 0.7 to 1.1 days in April.

GeologyThe major geological feature of theregion is the Rio Grande rift, whichresults from a period of crustal exten-sion that began between 32 and 27 mil-lion years ago, and is today distin-guished by faults and volcanoes andassociated mountains and basins(Chapin 1979). The ancestral RioGrande developed about 4 millionyears ago, following the course of thepre-established north-trending rift val-ley that extends from Colorado toMexico. The rift valley today consistsof a series of basins deeply filled withsediments from the nearby erodingmountains. Beginning about 780 000years ago, the ancestral Rio Grandebegan to erode through its own alluvialplain, and episodes of down-cuttingalternated with sediment deposition(Mack 1997). The river now occupiesan entrenched valley about 100 mlower than the surrounding, older sedi-mentary rocks.

The Texas portion of theMesilla Valley AVA is mostly underlainby Quaternary alluvium (sand, silt, clayand gravel) at lower elevations close tothe river in the west, and by older Qua-ternary alluvial deposits (gravel, sand,silt) to the east as elevation climbstoward the Franklin Mountains (Fig.14a). Deposits of Quaternary–Tertiaryclay, silt, sandstone, and conglomerateoccur locally at higher elevations,where they underlie the older Quater-nary alluvium. Some Quaternary sand

Table 6. Characteristics of predominant soil associations in the Texas DavisMountains American Viticultural Area.

Rock Brewster─ Musquiz─ Puerta─Predominant outcrop─ Rock Boracho─ Madrone─ Phantom─

Soil Mainstay─ outrcrop─ Santo Rock Rockhouse─Associations Liv Liv Tomas outcrop Hodgins

Area (hectares) 91 061 13 746 11 454 9431 1269Depth to bedrock 58 44 144 45 142

(cm)Texture Class loam (20) loam (20) loam (20) silt loam (20) loam (20)

– upperb

(depth, cm)Texture Classes other, clay, other, bedrock clay, clay clay clay loam

– lowerc other loamPermeability 8.69 8.52 4.12 6.62 2.84

– upperb (cm/hr)Permeability 8.65 10.8 3.07 4.97 6.25

– lowerc (cm/hr)pH – upperb 7 7 7.5 6.8 7.6pH – lowerc 7.2 7.5 7.5 6 7.8Available Water 4 3 12 4 13

Capacity (cm) 0-100 cm depthAvailable Water - - 18 - 20

Capacity (cm) 100-150 cm depthAvailable Water - - - - -

Capacity (cm) 150-250 cm deptha Source: Soil Information for Environmental Modeling and Ecosystem Management,

http://www.soilinfo.psu.edu, utilizing the CONUS-SOIL dataset based on the USDAState Soil Geographic Database (STATSGO).

b Depth from surface of upper soil layers having a uniform texture class; within a soil asso-ciation, permeability and pH values correspond to the same depth.

c Lower soil layers begin with the uppermost layer of a different texture class than theupper layers and extend to the full depth of the soil association.

18

sheet deposits are seen along the tran-sition zone between younger and olderalluvium, where elevation begins toclimb (Fig. 14a).

SoilsThe spatial distribution of the threepredominant soil associations in theMesilla Valley parallels the local geolo-gy (Fig. 14b). The Glendale–Armi-

jo–Harkey andPintura–Blue-point– Wink asso-ciations corre-spond to areasunderlain withyounger alluviumat lower elevationclose to the RioGrande; Delnorte–Canutio–Nickel isfound at higherelevations, general-ly correspondingto the area ofunderlying older

alluvium. Vineyards have been primarily

located within the area of the Glen-dale–Armijo–Harkey association,which comprise deep alluvial soils ofclay loam texture in the top 30 cm, andsandy loam beneath (Table 7). Thesesoils have a combination of drainageand water holding capacity that is well-suited to grape production. Permeabil-

ity is high: 5.68 cm/hr in the upper 30cm, and 9.09 cm/hr at lower depths.Available water capacity is 13 cm in theupper 100 cm and 37 cm in the lower150 cm. The Pintura–Bluepoint–Winkassociation has higher permeability andsomewhat lower available water capaci-ty, but is similarly favourable for grapeproduction. These alluvial soils arealso deep, but have a shallow (10 cm)upper layer of sand, underlain by sandyloam and more sand below. The pHof both these soil series is somewhathigh for grape production, rangingfrom 7.9 to 8.1, which may necessitatemanagement practices to avoid ironand zinc deficiency problems.

The Delnorte–Canutio–Nickelsoil series comprises deep sandy loamsoils with high permeability (15.6cm/hr) and low available water capaci-ty (Table 7). The generally dry natureof these soils can be difficult to man-age for grapes, requiring frequent irri-gation and careful monitoring of soiland vine water status.

Figure 13. Spatial distribution of a) elevation, b) annual pre-cipitation, c) cumulative growing degree-days, and d) meanAugust temperature in the Texas portion of the Mesilla ValleyAVA. The rectilinear patterns result from the relatively coarse(1 km) resolution of climatic data relative to the dimensionsof the Mesilla Valley AVA.

Figure 14. Spatial distribution of a) rock types, and b) soilassociations in the Texas portion of the Mesilla Valley AVA.Note: bolson deposits: lacustrine or fluviatile deposits of clay,silt, sand, and gypsum deposited in wide, flat, alluvium-floored intermontane basins or depressions.

GEOSCIENCE CANADA Volume 38 Number 1 March 2011 19

Grape and Wine ProductionThe Texas portion of the Mesilla Val-ley AVA has seen less vineyard andwinery development than within thisAVA in New Mexico. There are cur-rently two small wineries in this AVAin Texas, one with an estate vineyard(Zin Valle Vineyards; Fig. 15) produc-ing Zinfandel and Malvasia Bianca.The potential for development of newvineyards is highest in the western partof the AVA, at lower elevations closerto the Rio Grande; these areas have themost favourable combination of goodsoils and availability of irrigation water.

This area also fea-tures the lowestprecipitation, high-est GDD, andhighest RPMT.These factorsresult in good fruitripening condi-tions leading tohigh sugar accu-mulation, and lowdisease pressurefrom fungalpathogens.

SUMMARY ANDCONCLUSIONSThis research, uti-lizing the spatialanalysis of climate,topography, geolo-

gy, and soil, establishes a baselinedescription of wine-grape growingconditions within the four AmericanViticultural Areas of west Texas. Thefour AVAs share several common char-acteristics: high elevation (770 to 1600m), very warm to hot growing seasons(>2000 GDD), mild winter (Januaryaverage minimum -0.4 to -0.6°C), andlow annual precipitation (20 to 64 cm).

High elevation combined withlittle cloud cover produces high sun-light intensity that contributes to fruit-fulness of vines and good colour andtannin development in fruit. Cumula-

tive GDD in the coolest parts of theTexas High Plains AVA (2028) and theTexas Davis Mountains AVA (2190) arecomparable to the California wine-growing regions of the Sierra Foothillsand Lodi, respectively. It is noteworthythat wine grapes typically mature andare harvested in late August to earlySeptember in these west Texas AVAs,by which time degree-day accumula-tions are as much as 400 fewer thanstandard full-season (April to October)calculations used in comparisons toother winegrowing regions of theworld. The Mesilla Valley and Escon-dido Valley AVAs are warmer still, hav-ing 2830 and 2980 GDD, respectively.These AVAs would be classified as ‘toohot’ for wine production by Jones et al.(2010), but this conclusion is contra-dicted by more than 20 years of suc-cessful wine production in the Escon-dido Valley AVA. Again, early grapematurity and harvest (July and August)in the Mesilla Valley and EscondidoValley AVAs may preclude meaningfulcomparisons of full-season degree-days with other winegrowing regions.

The dry growing conditionsthroughout west Texas are advanta-geous for grape production becausethey are not conducive to spread ofmost fungal diseases of grapevines.Relatively low annual precipitation alsoenables irrigation practices to be usedto manage grapevine vigor and poten-tially influence grape quality. Wintertemperatures are generally mild, mak-ing possible the production of Vitisvinifera wine grapes with little risk offreeze injury. Recent vineyard plant-ings have focused on growing grapecultivars with known adaptation towarm and hot climates, including San-giovese, Vermentino and Tempranillo,and the Rhone cultivars Viognier,Grenache, Mourvèdre, and Syrah.

Soils are highly variable amongwest Texas AVAs. Vineyards are pre-dominantly planted on loamy finesands and fine sandy loams in theTexas High Plains AVA, whereas loamsand clay loams predominate in theother AVAs. The Texas High PlainsAVA leads the state in vineyardhectares and grape production, withmore than 440 ha and continuedgrowth underway. It also has the mostpotential for expansion, as more than1.25 million ha of deep, well-drained

Predominant Associationsa DelnortaCanutio Nickel

GlendaleArmijo Harkey

PinturaBluepoint

WinkArea (hectares) 6256 5640 4272Depth to bedrock (cm) 147 152b 152b

Texture Class– upperc (depth, cm) sandy loam clay loam (30) sand (10)

Texture Classes – lowerd sandy loam sandy loam sandy loam, sand

Permeability – upperc (cm/hr) 15.60 5.68 24.33

Permeability – lowerd (cm/hr) 15.60 9.09 15.90

pH – upperc 8.1 8.1 7.9

pH – lowerd 8.1 8.1 8.1Available Water Capacity (cm) 0-100 cm depth 5 13 9Available Water Capacity (cm) 100-150 cm depth 7 18 13Available Water Capacity (cm) 150-250 cm depth 7 19 15

dLower soil layers begin with the uppermost layer of a different texture class than the upper layers and extend to the full depth of the soil association.

Table 7. Characteristics of predominant soil associations in the Texas portion of the Mesilla Valley American Viticultural Area.

aSource: Soil Information for Environmental Modeling and Ecosystem Management, http://www.soilinfo.psu.edu, utilizing the CONUS-SOIL dataset based on the USDA State Soil Geographic Database (STATSGO).bValues of 152 cm indicate that bedrock was not encountered within this distance of the surface; actual depth to bedrock is undetermined.cDepth from surface of upper soil layers having a uniform texture class; within a soil association, permeability and pH values correspond to the same depth.

Figure 15. Zin Valle Vineyards with winery under construc-tion in 2004; Mesilla Valley AVA.

loamy fine sands, sandy loams, andloam soils are well-suited for grapeproduction.

The combination offavourable climatic conditions, plantingof climate-appropriate grape cultivars,and good vineyard soils has helpedestablish west Texas as a significantnew winegrowing region with demon-strated capability of producing highquality wines and great potential forsignificant expansion.

ACKNOWLEDGMENTSThe authors thank Andrew Birt andHyunsook Kim of the KnowledgeEngineering Laboratory at Texas A&MUniversity for contributions to thisresearch and development of theArcIMS application. We gratefullyacknowledge the critical review of thismanuscript and many helpful sugges-tions by R.W. Macqueen and L.D.Meinert.

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Received November 2009Accepted as revised September 2010

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