58 August 1999 New Mexico Geology

lish the age of the rock glaciers and to pre-sent a chronology based upon activity, and(4) to attempt to relate the distribution ofthe older and younger forms to climaticfluctuation and to the lithology and struc-ture of the pluton.

Geographic and geologic setting

The Capitan Mountains are located inLincoln County, New Mexico, approxi-mately 80 km northwest of Roswell and 40km northeast of Ruidoso in south-centralNew Mexico (Fig. 1). The range extends inan east-west direction for approximately32 km and is approximately 7 km wide.West Mountain is a nearly isolated uplandwith an altitude of 2,272 m and is separat-ed from the main part of the mountains byCapitan Gap (Fig. 2). The summit east ofCapitan Gap is 2,600–3,050 m in altitudeand rises approximately 900 m above thesurrounding alluvial-covered lowlands.The head of Hinchley Canyon and PierceCanyon Pass are well-defined saddles thatbreak the relatively flat crest (Fig. 3). Thesaddle at the head of Hinchley Canyondivides the range into western and easternsections, which have distinctive geologicand physiographic attributes noted below.Summit Peak and Capitan Peak are promi-nent landmarks above 3,050 m in the east-ern part of the range. The north and southflanks of the mountains are cut by numer-ous steep-walled canyons with maximumdepths of approximately 330 m. Manysmall canyons and ravines are tributariesto the larger canyons.

The Capitan Mountains are formed byan intrusion of mid-Tertiary age com-posed of alkali feldspar granite with con-tact zones that are poorly exposed exceptat the east and west ends (Allen andMcLemore, 1991). It is a single but textu-rally and compositionally zoned pluton

primary factors in the generation of rockglaciers (Morris, 1981). Frost wedgingsupplies the debris for the development ofrock glaciers and occurs under periglacialclimates that are characterized by fre-quently recurring freeze and thaw (Flint,1971, pp. 271–274; Washburn, 1980, pp.73–79). This process is promoted by snowcover of short duration and enough mois-ture in the ground for cryofraction tooccur (Corté, 1987). Climatic elementsconducive to the development of intersti-tial ice in rock glaciers are (1) sufficientprecipitation for the formation of the iceand (2) temperatures that are low enoughfor the maintenance and creep of the ice(Wahrhaftig and Cox, 1959). Interstitial ice(permafrost) can exist in rock glaciers ifthe mean annual temperature at groundlevel is 0– -1°C especially if the snow coveris thin and of short duration (Péwé, 1983).

Rock-glacier debris is derived primarilyfrom cliffs undergoing the blocky weath-ering that occurs in massive igneous,metamorphic, and sedimentary rockswhere two or three structural trends ofjoints are present (Evin, 1987). The processis particularly prevalent if two joint trendsare parallel and orthogonal to each otherand the other set is oblique. Well-devel-oped bedding planes in sedimentary rocksare also an important control. Frost wedg-ing is effective in dislodging blocks andslabs from cliffs with blocky structurebecause freeze-thaw action pries apartrock along joints, fractures, and beddingplanes.

The purpose of this paper is: (1) to pre-sent criteria for distinguishing rock glaci-ers of two ages in the Capitan Mountainsusing physiographic preservation and soildevelopment, (2) to note the geographicdistribution of the rock glaciers in rela-tionship to the textural and mineralogicalzones of the Capitan pluton, (3) to estab-

that ranges from a roof zone of gra-nophyric granite to an intermediate zoneof aplite to a core of porphyritic granite.The intrusion shows a progressive devel-opment from west to east of a coarse andporphyritic texture and an increase inmafic minerals. The textural and miner-alogical variations appear to be gradation-al with no evidence for multiple intru-sions.

The granophyre zone is fine grained(0.5–2 mm) and has a micrographic tex-ture. It encompasses an area from the westcontact zone to just east of Capitan Gapwhere it grades into an equigranular tex-tured aplite (Fig. 3). The aplite zoneextends eastward to the saddle at the headof Hinchley Canyon and also crops out atCapitan Gap where deeper parts of thepluton are exposed. The porphyry zonestretches from the saddle at the head ofHinchley Canyon to the east end of the

FIGURE 2—Location of the study area in the Capitan Mountains. Base map is the U.S. GeologicalSurvey’s topographic map of Roswell quadrangle 1:250,000 scale series.

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mountains and contains as much as 20%phenocrysts of anorthoclase and, rarely,plagioclase. The distribution of vein andbreccia deposits in the range indicates thatthe granophyre and aplite zones are moreintensely fractured than the porphyryzone (McLemore and Allen, 1991).

Rock-fall talus accumulates below cliffsand steep slopes, and frost rubble formsextensive sheets on the upper slopes of themountains; both obscure the bedrock inmany areas (Fig. 4). Some rubble sheetshave undulating surfaces formed by manysmall ridges and furrows. The ridges andfurrows are parallel to the contours indi-cating movement downslope because ofsolifluction or frost creep. Talus and frostrubble, nearly devoid of soil and vascularplants, cover approximately 30–60% ofslopes eroded in granophyre and aplitecompared to approximately 20–30% forslopes eroded in porphyry.

No long-term weather records exist forthe Capitan Mountains. Stations atArabela, Baca Ranger Station, and Capi-tan, however, suggest a mean annual pre-cipitation of 40–50 cm near the base(Gabin and Lesperance, 1977). The slopesmay receive 50–75 cm and the crest morethan 75 cm of precipitation annually (Tuanet al., 1969). Long-term weather recordsfrom Fort Stanton (Kunkel, 1984) and themean annual lapse rate of 0.72 cm/100 m

for south-central New Mexico (VanDevender et al., 1984) suggest the follow-ing approximations of current mean annu-al temperatures for the Capitan Moun-tains: 5–8°C for the slopes (2,300–2,750 m)and 3°C for the crest (3,000 m).

Vegetation zonation in the CapitanMountains ranges from desert grasslandnear the base to the spruce-fir associationon the crest (Martin, 1964). The pinyon-juniper association extends up to an aver-age altitude of approximately 2,200 m onthe lower slopes. The transition associa-tion is between approximately 2,200 and2,700 m, and the spruce-fir association isabove 2,750 m on the upper slopes andcrest. Aerial photographs reveal that theslopes and crest of the mountains are moreheavily forested in the eastern part of therange in porphyry terrane as compared tothe slopes and crest in the west in gra-nophyre and aplite terrane.

Description

One hundred twenty-four rock glaciersdeveloped below talus at the heads ofravines and small tributary canyons andon the floors of major canyons on thenorth and south sides of the CapitanMountains (Fig. 5). Blagbrough (1976,1991) observed the distribution of rockglaciers throughout the range but only

described the forms in the western part ofthe range in detail. The average altitude ofthe heads is approximately 2,574 m, andthe average altitude of the fronts is2,474 m (Table 1). The lengths are between56 and 1,565 m (Table 1), and the widthsaverage approximately 70 m. The rockglaciers in ravines and tributary canyonsare the extensions of talus at the drainageheads. Those on the floors of majorcanyons are composed of talus that accu-mulated as sheets along the base of sidewalls and head walls. Frost rubbleencroaches upon the heads and flanks ofmany rock glaciers on canyon floors andsuggests downslope movement of debrisafter the rock glaciers became inactive(Fig. 6).

The rock glaciers have steep fronts 5–60m high that slope approximately 30° (Fig.7). Heads merge with talus on the steepmountain slopes, and the surfaces abovethe fronts slope downstream at approxi-mately 15°. Flanks are steep embankments5–10 m high and commonly are separatedfrom the sides of canyons and ravines bygullies. Lateral ridges 1–5 m high delin-eate the flanks of many rock glaciers andbend to form transverse ridges at the crestof the fronts. On many rock glaciers,depressed areas are 1–5 m below lateralridges and extend from the crest of thefronts to the heads. Longitudinal and

FIGURE 3—East-west cross section along the south side of the Capitan Mountains showing major topographic features, distribution of the textural zones,and the areal extent of older and younger rock glaciers. Location of the textural zones is from Allen and McLemore (1991, p. 118, fig. 7). 1, average alti-tude of rock-glacier heads; 2, average altitude of rock-glacier fronts. Vertical exaggeration approximately x 2.6.

Hinchley CanyonSummit Peak

FIGURE 4—South side of the Capitan Mountains showing distribution of talus and frost rubble (light areas) east and west of Hinchley Canyon. Thedeposits are more extensive on slopes eroded in aplite west of the canyon than on slopes eroded in porphyry to the east. Photograph by Francis G. Varney.

60 August 1999 New Mexico Geology

transverse ridges and furrows are com-mon surface features that result in a hum-mocky topography with a relief of approx-imately 3 m on some surfaces. Conicalpits, with a mean depth of approximately3 m, and oblique ridges and furrows thattrend at approximately 45° to the apparentdirection of movement are less commonlydeveloped.

Rock glaciers of two ages are distin-guished based upon the preservation ofthe topographic expression and soil devel-opment. Thirty-eight older rock glaciers

are present in the eastern part of themountains below slopes eroded in por-phyry (Table 2). They are moderately dis-sected and show good preservation of thetongue-shaped form. The gross features,such as steep fronts, flanks, lateral ridges,and depressed areas, are somewhat sub-dued. Longitudinal and transverse ridgesand furrows are either poorly defined orunrecognizable on aerial photographs.The debris of the rock glaciers is formedfrom blocks and clasts of porphyry withaverage diameters of 30–90 cm.

Soil and vascular plants cover 50–85% ofthe surfaces on the older rock glaciers. Thesoil is composed of a dark-gray eolianmantle overlain by a dark-brown horizonformed by decomposed or partiallydecomposed organic material (Fig. 8). Theeolian mantle is 20–30 cm thick and com-posed primarily of fine sand and silt withlarger fragments that range to pebble size.The clasts are angular grains of quartz andfeldspar, and no well-rounded, frostedquartz grains were observed. The grainsare not coated with either organic stain orcalcium carbonate and appear extremelyfresh. The eolian mantle contains largeamounts of organic material possibly withsome calcium carbonate. The upper hori-zon is approximately 7.5 cm thick andcomposed of large wood fragments anddecomposed organic debris. It also con-tains sand and silt grains similar to thosein the eolian mantle.

The head of an older rock glacier is over-ridden by the front of a younger form inLas Tablas Canyon on the north side of therange (Fig. 9). The older rock glacier iscomposed of two talus tongues, both ofwhich have well-defined fronts andflanks. The surface is covered by an eolianmantle with a maximum thickness ofapproximately 30 cm overlain by approxi-mately 7.5 cm of decomposed to partlydecomposed organic debris. The front ofthe younger rock glacier rises abruptlyabove the older surface, and debris fromthe base extends into the depressed area ofthe upper tongue of the older form (Fig.10).

Seventy-two younger rock glaciers arepresent on West Mountain and in the mainupland of the Capitan Mountains betweenCapitan Gap and the saddle at the head ofHinchley Canyon below slopes eroded ingranophyre and aplite. Fourteen younger

FIGURE 5—Localities of older and younger rock glaciers in the Capitan Mountains. Rock-glacier symbols denote positions of the fronts. Base maps arethe U.S. Geological Survey’s topographic maps of Capitan Pass, Capitan Peak, Encinoso, and Kyle Harrison Canyon 71⁄2-min quadrangles.

TABLE 1—Comparative altitudinal and morphological data for rock glaciers in the Capitan Moun-tains.

All rock Rock glaciers Rock glaciersglaciers north side south side

Number 124 72 52

Mean altitude 2,474 2,443 2,517of fronts (m)

Range in altitude 2,244–2,689 2,244–2,659 2,378–2,689of fronts (m)

Mean altitude 2,574 2,542 2,605of heads (m)

Range in altitude 2,305–2,841 2,305–2,841 2,427–2,829of heads (m)

Mean length (m) 305 306 288

Range in length (m) 56–1,565 56–1,565 62–1,105

TABLE 2—Numbers of older and younger rock glaciers in the eastern and western parts of theCapitan Mountains.

Eastern section Western sectionporphyry terrane aplite and granophyre

terrane

Older rock glaciers 38 0

Younger rock glaciers 14 72

62 August 1999 New Mexico Geology

forms in the eastern part of the range arebelow slopes eroded in porphyry. Theyounger rock glaciers have a well-pre-served tongue-shaped form and are lessdissected than the older rock glaciers. Thefronts, flanks, lateral ridges, and de-pressed areas are well defined and showlittle modification by erosion (Fig. 7). Thelongitudinal and transverse ridges andfurrows are sharp and easily recognizableon aerial photographs.

The younger rock glaciers in the westernpart of the range are composed of debrisderived from granophyre and aplite. Theangular blocks and slabby clasts range indiameter from 15 cm to 2 m and averageapproximately 60 cm. Many smaller frag-ments are less than 30 cm in diameter andmay have been transported by water. Thedebris on the lateral ridges commonly islarger than that on the frontal faces and inthe depressed areas. Most fragments areoxidized, and some have undergone frostshattering while on the surfaces of rockglaciers. The debris is stable, and lichenscover 20–30% of exposed faces.

Eighteen rock glaciers on canyon floorswest of Summit Peak have arcuate ridgesand furrows along the flanks, which sug-gest that they developed from lobate rockglaciers that coalesced on the canyon floor.Seven younger rock glaciers east ofSummit Peak are composed of two talustongues, both of which have steep fronts,lateral ridges, and depressed areas. Theupper tongue appears to have overriddenthe head of the lower. Both tongues have

about the same degree of preserved sur-face features and about the same amountof area covered by soil and vegetation,which implies that they formed during asingle periglacial episode.

Soil and vascular plants usually coverapproximately 1–15% of the surfaces ofyounger rock glaciers. The soil is similar tothe upper horizon on the older rock glaci-ers and has an average thickness ofapproximately 7.5 cm in the western partof the range. It is dark brown in color andis formed by decomposed and partiallydecomposed organic material mixed withsand and silt. It fills voids between theblocks and slabby clasts. Trees and shrubsgrow in the soil and project through thedebris on some surfaces.

Age

No direct dating methods exist for therock glaciers in the Capitan Mountains atthe present time. Age inferences, however,can be made using paleoclimatic datafrom the Estancia Basin in central NewMexico (Hawley, 1993) and the glacial andperiglacial deposits on Sierra Blanca Peakin south-central New Mexico (Richmond,1986). Allen (1991) and Allen andAnderson (1993) have established a lateWisconsin chronology for pluvial LakeEstancia in the Estancia Basin using radio-carbon dating of organic remains anddetailed studies of basin-fill stratigraphyand sedimentology (Table 3). Bachhuber(1989) dates the initial fresh-water phase

of Lake Estancia at 24.3 ka, which marksthe onset of cold/moist conditions. Healso presents evidence for a long preced-ing cold/dry sub-pluvial interval, whichhe correlates with the early and middleWisconsin periods.

Allen (1991) recognized two major highstands for the lake. The older occurredbetween 20 and 15 ka during late Wiscon-sin maximum glacial conditions. It wasfollowed by a low stand between 15 and14 ka when warmer and drier conditionsprevailed. The younger high stand beganabout 13.7 ka and was followed by signif-icant desiccation of the lake between 12and 11 ka. A minor rise in the lake level atabout 10.5 ka is recorded before the finaldesiccation phase, which was apparentlyunderway by about 10 ka.

Glacial moraines were reported in analpine valley and small cirque on thenortheast side of Sierra Blanca Peak(Richmond, 1963, 1986). Richmond (1963)mapped two older moraines of probableBull Lake age and three younger morainesthought to be Pinedale (late Wisconsin) inage. The Bull Lake moraines are character-ized by broad crests, smooth slopes, andbroadly scattered surface boulders. Theybear mature soils approximately 90 cmthick with a well-developed B horizon.Pinedale moraines have irregular form,abundant surface boulders, and immaturesoils approximately 25 cm thick. Becauseof differences in surface form and boulderfrequency, Shroba (1977) suggested thatpart of the inner Bull Lake moraine of

FIGURE 10—Older rock glacier overridden by the front of a younger form in Las Tablas Canyon on the north side of the Capitan Mountains. The man inthe center of the photograph is at the contact of the older and younger debris. The surface of the older rock glacier is obscured by soil and vegetation,whereas the front of the younger form is nearly devoid of soil and vegetation. Photograph by John C. Varney.

New Mexico Geology August 1999 63

Richmond is Pinedale in age.Shroba (1977, 1991) describes two rock-

glacier deposits on Sierra Blanca Peak. Theolder is thought to be late Pinedale in age(about 14 ka) and was previously mappedas Pinedale till by Richmond (1963).According to these interpretations twoBull Lake moraines and two Pinedalemoraines are present. The older rock glac-ier is covered by a loessal matrix 60–110cm thick and is probably latest Pinedale inage. The deposit extends approximately800 m through the Pinedale moraines andpart way through the Bull Lake morainesand may have formed during the reces-sional episode of the Pinedale glaciation.The younger rock glacier may be TempleLake in age (about 12 ka). It is a smalldeposit approximately 125 m in lengthnear the cirque headwall and is mantledby approximately 40 cm of Holocene loess.

The younger Pinedale moraine on SierraBlanca Peak may be correlative with theglacial maximum high stand of LakeEstancia. The older rock-glacier deposit onSierra Blanca Peak probably was activenear the beginning of the younger highstand of Lake Estancia, and the youngerrock glacier may have been formed at theclose of the younger high stand as sug-gested by the dates cited for the two areas.Much of the loessal matrix on the rock-glacier deposits may have accumulatedduring the desiccation phase (12–11 ka) ofLake Estancia when warmer and drierconditions prevailed.

Blagbrough (1991) noted that the soils onthe younger rock glaciers in the CapitanMountains are similar to those on theTemple Lake moraines (12 ka) of Rich-mond (1963) in the Sangre de CristoMountains of northern New Mexico.Nonetheless, these forms may be lateWisconsin in age (about 14 ka) because ofthe time involved in the accumulation offines on the surface. In addition, theperiglacial record in the cirque on SierraBlanca Peak indicates only minimal cool-ing during Temple Lake time (12 ka),which would seem to preclude the preser-vation of interstitial ice in the CapitanMountains. The sharp constructional reliefand restrictive development of soil andvascular plants on the younger formsimplies movement near the close of thelate Wisconsin (about 14 ka).

The climatic history of the region sug-gests that the younger rock glaciers in theCapitan Mountains may be correlativewith the older rock glacier on SierraBlanca Peak and the beginning of theyounger high stand of Lake Estancia (13.7ka; Table 3). The thick cover of loessalmatrix (60–110 cm) on the older rock glac-ier deposit on Sierra Blanca Peak as com-pared to a soil cover of about 7.5 cm on theyounger rock glacier in the CapitanMountains can be explained by the 1,000m difference in altitude between the twoareas. Periglacial conditions probably

were much more severe and of longerduration at the higher altitudes on SierraBlanca Peak resulting in barren mountainslopes above timber line exposed to winderosion for long periods of time.

Blagbrough (1991) suggested that theolder rock glaciers in the CapitanMountains were of Bull Lake age using theglacial chronology on Sierra Blanca Peak.They are now hypothesized to be of lateWisconsin age (20–15 ka) because of thegood preservation of the gross featuresand weak soil development. Thus, theymay be contemporaneous with theyounger Pinedale moraine on SierraBlanca Peak and the glacial maximumhigh stand of Lake Estancia. The eolianmantle on the older forms may have beendeposited during the warm/dry episodethat followed the maximum high stand ofLake Estancia.

Discussion

The distribution of talus and frost rubblein the Capitan Mountains indicates thatthe granophyre and aplite zones are moresusceptible to freeze-thaw action than theporphyry zone. Production of debrisappears to be controlled by the chemicalcomposition and intensity of fracturing ofthe pluton when favorable climatic condi-tions exist. The heavy forest growth in theeastern part of the range may be related to

the mafic minerals in the pluton at thatlocality. More intense chemical weather-ing of the bedrock apparently results inthicker soil, which promotes forestgrowth. The thicker soil helps protect thebedrock from freeze-thaw action andrestricts the formation of talus and frostrubble east of the saddle at the head ofHinchley Canyon. The scarcity of soil, aswell as the well-developed fracture sys-tem, in the granophyre and aplite zonesenables blocks and slabs to be dislodgedeasily by frost action, resulting in the gen-eration of large volumes of debris.

The characteristics of rock glaciers in theeastern part of the Capitan Mountainsindicate two late Wisconsin periglacialepisodes separated by a period of warmerand drier conditions. The climate underwhich the older rock glaciers were gener-ated was of sufficient intensity and dura-tion to produce large volumes of talus andto mobilize the talus into rock glaciersbelow slopes eroded in porphyry. Thesnow cover probably was thin and of shortduration, which favored intense freeze-thaw action. The mean annual tempera-ture was below freezing, which resulted inthe formation and preservation of intersti-tial ice.

The earlier periglacial episode was fol-lowed by warmer and drier conditions,which terminated rock-glacier activity and

TABLE 3—Tentative correlation of late Wisconsin pluvial, glacial, and periglacial events in south-central New Mexico.

Estancia Basin Sierra Blanca Peak CapitanKa (Allen, 1991) (Richmond, 1986) Mountains

(Shroba, 1991) (This report)

10Minor high stand

(ca 10.5–10 ka)11

Desiccation(ca 12–11 ka)

12 Younger rock glacier(ca 12 ka)

13 Younger high stand(ca 13.7–12 ka)

14 Older rock glacier Younger rock glaciersLow stand (ca 14 ka)

(ca 15–14 ka)15 Loess

16

17 Glacial maximum Younger Pinedale Older rockhigh stand moraine glaciers

(ca 20–15 ka)18

19

20

64 August 1999 New Mexico Geology

initiated a period of eolian deposition onthe older surfaces. The composition andtexture of the sand and silt grains in theeolian mantle suggest that it was locallyderived from the erosion of the plutonand/or from alluvial deposits around thebase of the mountains.

A later periglacial episode resulted inthe generation of 14 younger rock glaciers,possibly at localities where the porphyryis more intensely fractured. The presencein Las Tablas Canyon of an older rockglacier down canyon from the front of ayounger form suggests that the laterperiglacial episode was less severe and/orof shorter duration than the earlierepisode. This hypothesis is supported bythe stratigraphic record in the EstanciaBasin, which demonstrates that the climat-ic changes during the full glacial highstand were more profound and of longerduration than those of the younger highstand (Allen, 1991; Allen and Anderson,1993).

Near the close of the late Wisconsin(about 12 ka) the climate again moderatedand resulted in the cessation of processesthat formed rock glaciers. The organicdebris on the older and younger rock glac-iers probably formed during the Holocene(11 ka to present) when warmer condi-tions prevailed. The presence of partiallydecomposed organic debris indicates thatthe process continues at the present time.

The absence of observable rock glacierswith the characteristics of older forms inthe western part of the Capitan Mountainsimplies one of three possibilities: (1) theolder rock glaciers never formed; (2) theyformed but were completely overriddenby younger rock glaciers during the laterperiglacial episode; or (3) they were gen-erated during the earlier periglacialepisode, became inactive when less severeconditions prevailed, and were reactivat-ed during the later episode. Because apliteand granophyre are more susceptible tofreeze-thaw action than porphyry, it isprobable that rock glaciers developed inthe western part of the range when olderforms were being generated in the east.No younger rock glaciers either situatedup valley from or overriding the heads ofolder forms were observed either in thefield or on aerial photographs in the west-ern part of the range. If older rock glaciersexist in the west, they are completely cov-ered by younger forms, which seemsunlikely if the earlier periglacial episodewas more severe and/or of longer dura-tion than the later episode.

Conclusions

Physiographic criteria and soil develop-ment may be used to distinguish rockglaciers of two ages in the CapitanMountains. Physiographic expression andsoil development suggest a late Wisconsinage and indicate two periglacial episodes

separated by a period of warmer and drierconditions. The distribution of older andyounger forms appears to be controlled bystructure and lithology of the bedrock,although the younger forms in the easternpart of the mountains are not clearlyunderstood. The absence of observablerock glaciers showing the characteristicsof older forms in the western part of therange also is subject to interpretation butmay be due to the reactivation of olderforms during the later periglacial episode.The older rock glaciers in the eastern partof the range were not reactivated duringthe less severe climate of the later peri-glacial episode because granite prophyryis less susceptible to freeze-thaw actionthan the aplite and granophyric granite tothe west, which resulted in a scarcity ofblocky debris necessary for rock-glaciermovement. The rock glaciers suggest alate Wisconsin climatic history for theCapitan Mountains comparable to thatindicated by glacial and periglacialdeposits on Sierra Blanca Peak and thesedimentary record in the Estancia Basin.Detailed mapping of and an extensive soilsampling program on the forms in theeastern part of the range may indicate amore complex late Wisconsin history thanthat presented in this paper.

ACKNOWLEDGMENTS—The author wishesto extend his appreciation to William O.Hatchel, Francis G. Varney, and John C.Varney who assisted in the field, and toLeigh L. Sprague who provided an aerialreconnaissance of the Capitan Mountains.Thanks are due also to David W. Love forhis laboratory examination and interpreta-tion of the soil samples. The manuscriptgreatly benefited from the critical reviewand comments of Paul A. Catacosinos,David W. Love, John D. Vitek, and SidneyE. White. Support for the early stages ofthe field investigation was provided bythe Geological Society of America researchgrant 1239-69.

References

Allen, B. D., 1991, Effects of climatic change onEstancia Valley, New Mexico: sedimentationand landscape evolution in a closed-drainagebasin; in Julian, B., and Zidek, J. (eds.), Fieldguide to geologic excursions in New Mexicoand adjacent areas of Texas and Colorado:New Mexico Bureau of Mines and MineralResources, Bulletin 137, pp. 166–171.

Allen, B. D., and Anderson, R. Y., 1993, Evi-dence for rapid shifts in climate during thelast glacial maximum: Science, v. 260, pp.1920–1923.

Allen, M. S., and McLemore, V. T., 1991, Thegeology and petrogenesis of the Capitan plu-ton, New Mexico; in Barker, J. M., Kues, B. S.,Austin, G. S., and Lucas, S. G. (eds.), Geologyof the Sierra Blanca, Sacramento, and Capitanranges, New Mexico: New Mexico Geo-logical Society, Guidebook 42, pp. 115–127.

Bachhuber, F. W., 1989, The occurrence andpaleolimnologic significance of cutthroat

trout (Oncorhynchus clarki) in pluvial lakes ofthe Estancia Valley, central New Mexico:Geological Society of America, Bulletin, v. 10,pp. 1543–1551.

Blagbrough, J. W., 1976, Rock glaciers in theCapitan Mountains, south-central NewMexico (abs.): Geological Society of America,Abstracts with Programs, v. 8, pp. 570–571.

Blagbrough, J. W., 1991, Late Pleistocene rockglaciers in the western part of the CapitanMountains, Lincoln County, New Mexico:description, age and climatic significance; inBarker, J. M., Kues, B. S., Austin, G. S., andLucas, S. G. (eds.), Geology of the SierraBlanca, Sacramento, and Capitan ranges,New Mexico: New Mexico Geological Society,Guidebook 42, pp. 333–338.

Corté, A. E., 1987, Rock glacier taxonomy; inGiardino, J. R., Shroder, J. F., Jr., and Vitek, J.D. (eds.), Rock glaciers: Allen and Unwin,Boston, pp. 27–39.

Evin, M., 1987, Lithology and fracturing controlof rock glaciers in southwestern Alps ofFrance and Italy; in Giardino, J. R., Shroder, J.F., Jr., and Vitek, J. D. (eds.), Rock glaciers:Allen and Unwin, Boston, pp. 83–106.

Flint, R. F., 1971, Glacial and Quaternary geolo-gy: John Wiley and Sons, New York, 892 pp.

Gabin, V. L., and Lesperance, L. E., 1977, NewMexico climatological data: W. K. Summersand Associates, Socorro, 436 pp.

Giardino, J. R., and Vitek, J. D., 1988, The signif-icance of rock glaciers in the glacial-periglacial landscape continuum: Journal ofQuaternary Science, v. 3, pp. 97–103.

Hawley, J. W., 1993, Geomorphic setting andlate Quaternary history of pluvial-lake basinsin the southern New Mexico region: NewMexico Bureau of Mines and MineralResources, Open-file report 391, 28 pp.

Kunkel, K. E., 1984, Temperature and precipita-tion summaries for selected New Mexicolocations: New Mexico Department ofAgriculture, Las Cruces, 190 pp.

Martin, W. C., 1964, Some aspects of the naturalhistory of Capitan and Jicarilla Mountains,and Sierra Blanca Peak region of New Mex-ico; in Ash, S. R., and Davis, L. V. (eds.),Ruidoso country: New Mexico GeologicalSociety, Guidebook 15, pp. 171–176.

McLemore, V. T., and Allen, M. S., 1991,Geology of mineralization and associatedalteration in the Capitan Mountains, LincolnCounty, New Mexico; in Barker, J. M., Kues, B.S., Austin, G. S., and Lucas, S. G. (eds.),Geology of the Sierra Blanca, Sacramento,and Capitan ranges, New Mexico: NewMexico Geological Society, Guidebook 42, pp.291–298.

Morris, S. E., 1981, Topoclimatic factors and thedevelopment of rock-glacier facies, Sangre deCristo Mountains, southern Colorado: Arcticand Alpine Research, v. 13, pp. 329–338.

Péwé, T. L., 1983, The periglacial environmentin North America during Wisconsin time; inPorter, S. C. (ed.), Late Quaternary environ-ment of the United States, v. 1, The latePleistocene: University of Minnesota Press,Minneapolis, pp. 157–189.

Richmond, G. M., 1963, Correlation of someglacial deposits in New Mexico: U.S.Geological Survey, Professional paper 450-E,pp. E121–E125.

Richmond, G. M., 1986, Stratigraphy and corre-lation of glacial deposits of the RockyMountains, the Colorado Plateau, and the

New Mexico Geology August 1999 65

ranges of the Great Basin; in Sibrava, V.,Bowen, D. Q., and Richmond, G. M. (eds.),Quaternary glaciation in the northern hemi-sphere: Pergamon Press, New York, pp.99–127.

Shroba, R. R., 1977, Soil development inQuaternary tills, rock glacier deposits, andtaluses, southern and central RockyMountains: Unpublished PhD dissertation,University of Colorado, Boulder, 424 pp.

Shroba, R. R., 1991, Major trends in soil devel-opment and soil-clay mineralogy in lateQuaternary surficial deposits at Sierra BlancaPeak, south-central New Mexico (abs.):Geological Society of America, Abstracts withPrograms, v. 23, no. 4, p. 94.

Tuan, Y. F., Everard, C. E., and Widdison, J. G.,1969, The climate of New Mexico: NewMexico State Planning Office, Santa Fe, 197pp.

Van Devender, T. R., Betancourt, J. L., andWimberly, M., 1984, Biogeographic implica-

tions of a packrat midden sequence from theSacramento Mountains, south-central NewMexico: Quaternary Research, v. 22, pp.344–360.

Wahrhaftig, C. A., and Cox, A. W., 1959, Rockglaciers in the Alaska Range: GeologicalSociety of America, Bulletin, v. 70, pp.383–436.

Washburn, A. L., 1980, Geocryology: A surveyof periglacial processes and environments:John Wiley and Sons, New York, 406 pp.

White, S. E., 1981, Alpine mass movementforms (noncatastrophic): Classification,description, and significance: Arctic andAlpine Research, v. 13, pp. 127–137.

Geographic NamesU.S.Board on Geographic Names

South Sandia Spring—spring, in CibolaNational Forest/Sandia MountainWilderness, 2.4 km (1.5 mi) south ofSouth Sandia Peak, 1.1 km (0.7 mi) eastof Three Gun Spring, 4 km (2.5 mi)northwest of Tijeras; Sandovol County,NM; sec. 8 T10N R5E, NMPM;35°05’56”N, 106°25’32”W; USGS map,Tijeras 1:24,000.

Steins Peak—summit, elevation 1,786 m(5,861 ft), on the south side of DoubtfulCanyon, 12.5 km (7.8 mi) north–north-west of Steins, 0.8 km (0.5 mi) east of theArizona State boundary; named forMajor Enoch Steen (1800–1880); HidalgoCounty, NM; sec. 6 T23S R21W, NMPM;32°20’01”N, 109°02’ 35”W; USGS map,Doubtful Canyon 1:24,000; not SteensPeak.

Bald Knoll Tank—reservoir, 38 m (125 ft)by 30 m (100 ft), in Gila National Forest,along the west slope of the Big BurroMountains, 1.9 km (1.2 mi) northeast ofJoe Harris Spring, 4 km (2.5 mi) north-west of Bullard Peak; Grant County,NM; sec. 23 T18S R17W, Gila and SaltRiver Meridian; 32°43’29”N, 108°34’25”W; USGS map, Bullard Peak 1:24,000;not Bold Tank.

Burnt Mill Canyon—valley, 3.2 km (2 mi)long, in Cibola National Forest, heads at35°11’26”N, 108°25’13”W, trends south-west to a point 6.3 km (3.9 mi) northeastof the community of Ramah, 6.4 km (4mi) north of Wild Sheep Mesa; CibolaCounty, NM; secs. 20, 17, 16, 9 & 10 T11NR15W, NMPM; 35°10’17”N, 108°26’35”W; USGS map, Ramah 1:24,000; notOak Hollow.

Kelly Tank—reservoir, 61 m (200 ft) by 53m (175 ft), in Gila National Forest,between Park Canyon and Burro SpringCanyon, 8 km (5 mi) south–southwest ofBullard Peak; Grant County, NM; sec. 23T19S R17W, Gila and Salt RiverMeridian; 32°38’20”N, 108°34’16”W;USGS map, Bullard Peak 1:24,000; notBurro Spring Tank.

Oak Hollow—valley, 4 km (2.5 mi) long,in Cibola National Forest, heads at35°11’44”N, 108°23’04”W, trends south-west to a point 8 km (5 mi) northeast ofthe community of Ramah; CibolaCounty, NM; secs. 14, 15 & 22 T11NR15W, NMPM; 35°10’05”N, 108°24’55”W; USGS map, Ramah 1:24,000.

Richardson Tank—reservoir, 53 m (175 ft)by 30 m (100 ft), in Gila National Forest,along Burro Spring Canyon, 8.9 km (5.5mi) south–southwest of Bullard Peak;Grant County, NM; sec. 23 T19S R17W,Gila and Salt River Meridian; 32°38’04”N, 108°34’14”W; USGS map, BullardPeak 1:24,000; not Richard Tank.

—David McCrawNMBMMR Correspondent