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NVREC-09 Project 3.3.1 Contract # EE0000272

Geothermal Prospecting: Relationships Between Regional Heat Flow and Isostatic Rebound Patterns in the Great Basin

Kenneth D. Adams Final Report

January 18, 2011 Summary

There has been up to 22 m of differential isostatic rebound in the Lake Lahontan basin of northwestern Nevada and adjacent northeastern California after removal of the late Pleistocene water load. In general, the rebound pattern prescribes a large domal uplift, with the highest elevated shorelines adjacent to the largest water bodies, but clear anomalies in this pattern exist. This study uses the pattern of rebound and associated anomalies to infer areas of relatively high heat flow and geothermal potential in the Lahontan basin. Many geologic and geophysical tools and datasets have been previously used to infer geothermal potential but no single tool or approach can accurately predict where economic geothermal resources will be found. Instead, multiple parameters are commonly combined to develop geothermal favorability or potential maps that indicate areas of high geothermal potential. When comparing the pattern of rebound anomalies to a recent geothermal potential map, there is a close correspondence between some of the high potential areas and positive rebound anomalies, but commonly the spatial extent of the anomalies cover a broader area than do the regions that have been mapped with the highest potential. This pattern may indicate that areas of highest potential are larger than have previously been mapped. The dataset of rebound anomalies presented here is intended to be another parameter that can be used in developing future favorability maps. Introduction

The Great Basin has long been recognized for its geothermal resources, evidenced by abundant thermal springs, high heat flow, and operating geothermal power plants. Some researchers, however, estimate that only about 20% of the region’s total accessible resource base has been identified, indicating that there are probably many more geothermal areas to be discovered (Brook et al., 1979; Richards and Blackwell, 2002). To accelerate geothermal energy development and use in the Great Basin, recent research efforts are utilizing a variety of approaches including structural and geophysical analyses (Blewitt et al., 2003; Faulds et al., 2002; Louie, 2004; Bell and Ramelli, 2007, 2009), geochemical characterization of thermal waters (Shevenell et al., 2002), and spatial modeling using a geographic information system (GIS) database (Coolbaugh et al., 2002, 2004; Zehner et al., 2010). All of these efforts are providing important information that will likely increase geothermal development and use in the Great Basin.

A potentially useful data set that has not been utilized for delineating geothermal potential, however, is the pattern of isostatic rebound induced by Pleistocene Lake Lahontan (Fig. 1). This data set represents a three-dimensional view of the strength of the Earth’s lithosphere across more than 80,000 km2 of the Lahontan basin. Because lithospheric strength is directly related to temperature, anomalies in the overall domal pattern of rebound (Fig. 1) may be associated with variations in heat flow not recognized through other exploration techniques. This pilot study

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examines the spatial relationships between rebound anomalies and existing geological, geophysical, and geothermal data with the goal of refining the boundaries of known geothermal resource areas in northwestern Nevada and potentially locating new geothermal areas where there is little to no surface expression.

Background

The following sections provide important background information on the relationships among geothermal phenomena, crustal and lithospheric properties, and the processes of isostatic rebound in the Great Basin.

Heat flow in the Great Basin: High heat flow within the Great Basin is a product of the interrelated effects of Cenozoic extension and late Cenozoic intrusion and volcanism (Blackwell, 1983; Morgan and Gosnold, 1989). Although several late Cenozoic volcanic centers exist within the Lahontan basin, many but not all of the geothermal systems appear to be associated with normal faulting during the Quaternary (Blewitt et al., 2003; McKenna and Blackwell, 2004). In this model, fluids circulate deep within the crust and convect heat back near the surface along permeable faults. Conduction from these fluids into surrounding materials can result in broad thermal aureoles around geothermal systems (Richards and Blackwell, 2002). Thus, hot springs, fumaroles, and other evidence of high temperatures often characterize active geothermal systems. Some systems, however, have little to no surface expression and are difficult to relate to specific structures (e.g., Desert Peak; Benoit et al., 1982).

Overall, the Lahontan basin is characterized by relatively high heat flow (Lachenbruch and Sass, 1978; Blackwell, 1983; Blackwell and Richards, 2004) and contains most of the high temperature geothermal plants in the Great Basin. Early studies defined the Battle Mountain heat flow high as a NE-SW trending zone of elevated heat flow extending from near Battle Mountain southwest to the Reno area. A recent compilation of data by Blackwell and Richards (2004) suggests that the pattern of heat flow in the western Great Basin is complex and appears to vary greatly in a lateral sense. Accurate definition of these gradients, however, is limited by the density, or lack thereof, of heat flow measurements and other thermal data.

Measurement of heat flow over an area is complicated by local groundwater circulation (Lachenbruch, 1978; Blackwell, 1983; Richards and Blackwell, 2002). Hot water migrating up from depth can be completely masked by laterally flowing cooler groundwater near the surface. In this situation and in places where groundwater is deep, there may be little to no surface expression of a geothermal system—making discovery and development of these types of systems particularly challenging.

There are many different types of thermal data including distribution of thermal springs and wells, temperature gradients in wells, heat flow measurements, and well and spring geothermometry. Not all of these data types provide equally valuable information. The recent map and database by Coolbaugh et al. (2004) shows spatial relationships among different thermal data sets and physical features within the Great Basin. From this map, it is clear that no single data set is completely effective in indicating the location and extent of geothermal systems. Instead, this is a prime example of how multiple data sets can be combined to gain a better understanding of the geothermal potential of the Great Basin.

Crustal and lithospheric properties: The Lahontan basin straddles the boundary between the Walker Lane belt (Stewart, 1988) and Basin and Range province. Ongoing deformation is expressed by abundant late Pleistocene and younger fault scarps throughout the basin (Dohrenwend et al., 1996) and multiple historic ruptures in the central Nevada seismic belt

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(Callaghan and Gianella, 1935; Gianella and Callaghan, 1934a, b; Slemmons, 1957a, b; Wallace, 1984a; Caskey et al., 1996) and elsewhere in the region. Wallace (1984b) referred to most of the Lahontan basin as the “Black Rock-Carson Sink zone of extension” and inferred that the area has undergone greater and possibly more rapid extension than surrounding areas in late Tertiary time. Ongoing geodetic surveys indicate that this trend has continued to the present (Bennett et al., 1998; Bennett et al., 1999; Thatcher et al., 1999; Blewitt et al., 2003), suggesting that the crust may be thinner beneath the Lahontan basin than in surrounding areas.

Across the Lahontan basin, new seismic data indicate that crustal thickness ranges between about 24 and 44 km with areas of thinner crust trending NW-SE along the Walker Lane belt and NE-SW along the Humboldt structural zone (Louie, 2004). These zones of thinner crust generally correspond to regions of higher heat flow, as indicated by a variety of data including the locations of operating geothermal plants. Regions of thin crust are often characterized by high heat flow. The simplest explanation for this correlation is that regions in which crust has been thinned by extensional tectonics, as is the case in the Great Basin, also experience upward advection of hot material. Effectively, the temperature at the crust-mantle boundary remains constant, but that boundary is moved closer to the surface.

Strength of the lithosphere also is affected by variations in heat flow. In this context, the terms “crust” and “lithosphere” are related but should be viewed as different concepts. The crust is a compositionally distinct layer separated from the underlying mantle by a boundary known as the Mohorovicic discontinuity, or Moho. Velocity change occurs over a short enough depth range, in most places, that it causes reflection of obliquely incident seismic waves and thus allows easy discrimination of crustal thickness. The lithosphere, in contrast, is the mechanically strong part of the upper layers of the Earth and can be either entirely within the crust, coincident with the crust, or include parts of the underlying mantle.

Temperature is a major influence on the long-term strength of crust and mantle rocks. A 100 degree Celsius temperature increase, for example, can lead to several orders of magnitude decrease in effective viscosity. Therefore, variations in crustal temperature observed across the Lahontan basin should also correlate to variations in lithospheric strength. These variations in strength are likely expressed in the pattern of isostatic rebound caused by emplacement and removal of the Lake Lahontan water load.

Isostatic rebound in the Lahontan basin: The pattern of deformed shorelines in the Lahontan basin is a direct reflection of the strength of the lithosphere and the spatial-temporal loading history of the lake (Adams et al., 1999). Variations in lithospheric strength across the basin are difficult to measure directly by geophysical means but are recorded in the pattern of deformed shorelines. Detailed surveys of the highest late Pleistocene shoreline reveal that there is about 22 m of relief on this once horizontal (equipotential) surface (Adams et al., 1999) (Fig. 1). Active faulting in the Lahontan basin appears to have had little effect on the rebound signal. Although the rebound pattern is generally symmetrical around the basin, with the highest elevation shorelines adjacent to the largest former water bodies, discrete anomalies exist that depart from this generally smooth pattern (Fig. 2).

Viscoelastic modeling estimates that the effective elastic lithosphere beneath the Lahontan basin is about 20 km thick and that upper mantle viscosity is about 1018 Pa s (Bills et al., 2007). Both of these values are small by global standards but consistent with previous interpretations of a warm, extending crust. Although the viscoelastic modeling approach provides single, basin-wide estimates of lithospheric thickness and upper mantle viscosity (Bills et al., 1994; Bills et al.,

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2007), variations in these properties are likely across the 80,000+ km2 of the Lahontan basin (Fig. 2). Methods

The pattern of isostatic rebound in the Lahontan basin documented by Adams et al. (1999) was delineated on the basis of 177 surveyed high shoreline elevations (Fig. 1) that define a broad, domal pattern of uplift. Although this is a large number of observations, there are still parts of the basin that do not have adequate coverage (Fig. 1), particularly in some of the regions that have elevated heat flow. To better examine the spatial relationships between heat flow anomalies and rebound anomalies, the rebound anomalies needed to be better defined.

In this study, rebound anomalies are defined in two ways. The first is qualitative in the sense that departures in the overall pattern of rebound are noted, such as the steep decline in shoreline elevations at the north end of the basin (Fig. 1). In the second approach, anomalies are calculated by comparing the surveyed shoreline heights at a given location with their modeled elevations. The difference in elevations defines the apparent magnitude of the anomaly (Fig. 2). Positive anomalies are ones in which the elevations of surveyed shorelines are higher than the modeled elevations of those shoreline sites. Negative anomalies are when the surveyed elevations of shorelines are lower than their modeled elevations. In this context, anomalies are not typically defined by a single shoreline measurement but are usually expressed by several measurements in an area.

To better define the spatial extent of rebound anomalies, additional shoreline measurements were needed. In this study, only constructional beach features (e.g., spits, beach ridges, tombolos, etc.) were located and surveyed to stay consistent with the procedures outlined in Adams et al. (1999). The first step in the process was to locate potential survey targets by viewing high resolution imagery in Google Earth and in ArcGIS. Using this approach, approximately 190 potential shoreline measurement sites were located throughout the basin, but most in areas where heat flow anomalies exist.

In the study of Adams et al. (1999) a total station tied to local, geodetic benchmarks was used to survey shoreline elevations, which required lines-of-site between instrument placement, the benchmark, and the shoreline of interest. All three locations needed to be within 1-2 km of one another. In the present study, a Trimble Nomad single receiver, real time GPS system was used, which allowed greater flexibility in the locations of measurement sites because local benchmarks were not needed. The stated precision and accuracy of this instrument is several decimeters but repeatability tests were run to confirm these estimates. In the tests, a single point was resurveyed a total of six times over a period of two days. The results of this test indicated slightly worse results than the manufacturing claims, but all measurements were within 1m in the X, Y, and Z directions. Considering that the natural variability in the height of constructional shorelines with reference to a still-water datum is on the order of 2-3 meters (Adams and Wesnousky, 1998), the precision and accuracy of the Trimble Nomad was deemed acceptable. Using this survey device, 46 additional shoreline elevation sites were added to the rebound dataset (Fig. 1).

For the Walker Lake subbasin, airborne LIDAR was available. This high resolution topographic data allowed extraction of precise shoreline elevations from a raster dataset in an ArcGIS database, which was created to manage the spatial data collected in this project. A total of 38 elevations were extracted from the LIDAR data in the Walker subbasin and southern Carson Sink (Fig. 1), but with closer examination more measurements could be collected.

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Results

For this study, a total of 86 new shoreline elevation measurements were added to the existing dataset of Adams et al. (1999), which previously had a total of 177. Of the 86 new elevations, 47 were surveyed with a Trimble Nomad GPS instrument (Table 1) while 39 were extracted from LIDAR topographic data that was available for the Walker Lake subbasin and the southern Carson Sink (Fig. 1; Table 2). Direct comparisons between surveyed points and LIDAR-extracted points generally were favorable. Most of the surveyed points were collected in the western Lahontan basin in order to better define rebound anomalies.

Figure 2 presents a map of rebound residuals and inferred anomalies in the Lahontan basin. For this study, rebound anomalies were delineated from multiple shoreline measurement sites that have positive rebound residuals (measured elevations minus modeled elevations). In this interpretation, large, positive anomalies exist in the Walker Lake subbasin, in a broad zone extending north from Pyramid Lake, through the San Emideo Desert, and into the Black Rock Desert. Smaller positive anomalies are located in the northern part of the Lahontan basin, and in parts of the Humboldt-Carson Sink.

Figure 3 compares the distribution of rebound anomalies with shallow (0-1 km) temperature gradients. Although there is some agreement between positive rebound anomalies and high heat gradients, the correspondence is not very convincing.

Figure 4 compares the distribution of rebound anomalies to differences in crustal thickness. Again, although some of the positive rebound anomalies are underlain by relatively thin crust, the correspondence is not very close.

Figure 5 presents a map that shows the spatial distribution of positive rebound anomalies with respect to the geothermal potential map of Zehner et al. (2010) for the Lahontan basin. The map of Zehner et al. (2010) takes into consideration multiple data sources including the maximum temperature of known geothermal systems as well as the Geothermal Favorability Map of Coolbaugh et al. (2004). Correspondence between some of the anomalies and areas of high geothermal potential is significant. For example, the region extending from Pyramid Lake through the San Emideo Desert and north to the Black Rock Desert represents an area of super elevated shorelines coinciding with areas of known geothermal resources and high potential. Other rebound anomalies possibly coincident with geothermal areas include the northern Hot Springs Mountains, the Rye Patch Dam area, the Trego area, and the north end of the east arm of the Black Rock Desert (Figs. 2 and 5). Some of these spatial correlations also agree particularly well with the geothermal resources of Nevada map by Trexler et al. (1983). Prominent rebound anomalies that are not collocated with geothermal data include most of the Walker Lake subbasin. It is important to note that the rebound anomalies, as defined herein, commonly are larger than the high local potential zones defined by Zehner et al. (2010). Discussion and Conclusions

Virtually the entire Lahontan basin possesses relatively high heat flow, but only specific zones or regions within this area are economically viable for producing geothermal energy. The trick then is to be able to locate the areas where geothermal power plants are feasible. Many different datasets have been used to try to delineate the most favorable locations for geothermal resources, with the most recent being the map of Zehner et al. (2010). A Comparison of the distribution of positive rebound anomalies to the distribution of areas of different geothermal potential yields interesting results (Fig. 5). Several of the high local geothermal potential areas are collocated with positive rebound anomalies, but generally are more restricted in area. The observation that

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the boundaries of some of the rebound anomalies extend beyond the boundaries of high geothermal potential may indicate that there are larger areas within the Lahontan basin that have high potential for geothermal resources. In particular, the elevations of almost all shorelines in the Walker Lake subbasin suggest that a large rebound anomaly is present covering most of the basin, but there are just two relatively small areas of high potential mapped by Zehner et al. (2010). It may be possible, therefore, that other areas of high potential exist in the Walker Lake subbasin. Another large rebound anomaly extends from Pyramid Lake, through the San Emideo Desert, and into the Black Rock Desert. Within this zone are several high potential zones and operating geothermal plants, but the zones as mapped by Zehner et al. (2010) are discrete and localized. If rebound anomalies are reflective of thinner, hotter crust then these high potential zones might be larger than previously mapped.

To date, regional approaches to identifying geothermal resources have relied on the spatial relationships between multiple geologic, geochemical, and geophysical data sets (Coolbaugh et al., 2004; Zehner et al., 2010). No single data set points the way to economical geothermal resources, but in combination appear to delineate areas of high potential. In this study, the concept of isostatic rebound anomalies was developed and the distribution of these anomalies compared to favorability maps. By themselves, the distribution of rebound anomalies do not delineate areas of high geothermal potential but when used in combination with other data sets may help broaden and clarify the boundaries of these areas. References Adams, K. D., and Wesnousky, S. G., 1998, Shoreline processes and the age of the Lake

Lahontan highstand in the Jessup embayment, Nevada: Geological Society of America Bulletin, v. 110, no. 10, p. 1318-1332.

Adams, K. D., Wesnousky, S. G., and Bills, B. G., 1999, Isostatic rebound, active faulting, and potential geomorphic effects in the Lake Lahontan basin, Nevada and California: Geological Society of America Bulletin, v. 111, no. 12, p. 1739-1756.

Bell, J.W., and Ramelli, A.R., 2007, Active faults and neotectonics at geothermal sites in the western Basin and Range: Preliminary results:" GRC Transactions, v. 31, p. 375-378.

Bell, J.W., and Ramelli, A.R., 2009, Active fault controls at high-temperature geothermal sites: Prospecting for new faults: GRC Transactions, v. 33, p. 425-429.

Bennett, R. A., Davis, J. L., and Wernicke, B. P., 1999, Present-day pattern of Cordilleran deformation in the western United States: Geology, v. 27, p. 371-374.

Bennett, R. A., Wernicke, B. P., and Davis, J. L., 1998, Continuous GPS measurements of contemporary deformation across the northern Basin and Range province: Geophysical Research Letters, v. 25, no. 4, p. 563-566.

Benoit, D., Hiner, J. E., and Forest, R. T., 1982, Discovery and geology of the Desert Peak geothermal field: A case history: Nevada Bureau of Mines and Geology Bulletin 97, 82 p.

Benson, L. V., Currey, D. R., Lao, Y., and Hostetler, S. W., 1992, Lake-size variations in the Lahontan and Bonneville basins between 13,000 and 9000 (super 14) C yr B.P: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 95, no. 1-2, p. 19-32.

Benson, L., Kashgarian, M., and Rubin, M., 1995, Carbonate deposition, Pyramid Lake subbasin, Nevada; 2, Lake levels and polar jet stream positions reconstructed from radiocarbon ages and elevations of carbonates (tufas) deposited in the Lahontan Basin: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 117, no. 1-2, p. 1-30.

Bills, B. G., Adams, K. D., and Wesnousky, S. G., 2007, Viscosity structure of the crust and upper mantle in western Nevada from isostatic rebound patterns of Lake Lahontan

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shorelines: Journal of Geophysical Research, v. 112, no. B6, B06405, p. 10.1029/2005JB003941.

Blackwell, D., and Richards, M., 2004, Geothermal map of North America: AAPG. Blackwell, D., 1983, Heat flow in the northern Basin and Range Province, in Council, G. R., ed.,

The role of heat in the development of energy and mineral resources in the northern Basin and Range Province, special report 13, p. 81-93.

Blewitt, G., Coolbaugh, M., Sawatzky, D., Holt, W., Davis, J., and Bennett, R., 2003, Targeting of potential geothermal resources in the Great Basin from regional to basin-scale relationships between geodetic strain and geological structures: Geothermal Resources Council Bulletin, v. 27, p. 3-7.

Briggs, R. W., Wesnousky, S. G., and Adams, K. D., 2005, Younger Dryas and late Holocene lake stands in the Pyramid Lake subbasin of Lake Lahontan, Nevada, USA: Quaternary Research, in press.

Brook, C. A., Mariner, R. H., Mabey, D. R., Swanson, J. R., Guffanti, M., and Muffler, L. J. P., 1979, Hydrothermal convection systems with reservoir temperatures > 90 degrees C, in Muffler, L. J. P., ed., Assessment of Geothermal Resources of the United States-1978, U.S. Geological Survey Circular 790, 163 p.

Callaghan, E., and Gianella, V. P., 1935, The earthquake of January 30, 1934, at Excelsior Mountains, Nevada: Seismological Society of America Bulletin, v. 25, p. 161-168.

Caskey, S. J., Wesnousky, S. G., Zhang, P., and Slemmons, D. B., 1996, Surface faulting of the 1954 Fairview Peak (Ms 7.2) and Dixie Valley (Ms 6.8) earthquakes, central Nevada: Seismological Society of America Bulletin, v. 86, p. 761-787.

Condie, K. C., and Barsky, C. K., 1972, Origin of Quaternary basalts from the Black Rock Desert region, Utah: Geological Society of America Bulletin, v. 83, p. 333-352.

Coolbaugh, M., Taranik, J. V., Raines, G. L., Shevenell, L. A., Sawatzky, D., Bedell, R., and Minor, T. B., 2002, A geothermal GIS for Nevada; defining regional controls and favorable exploration terrains for extensional geothermal systems: Geothermal Resources Council Transactions, v. 26, p. 485-490.

Coolbaugh, M., Zehner, R., Kreemer, C., Blackwell, D., Oppliger, G. L., Sawatzky, D., Blewitt, G., Pancha, A., Richards, M., Raines, G. L., Johnson, G. L., and Minor, T. B., 2004, Preliminary geothermal map of the Great Basin, western United States: Great Basin Center for Geothermal Energy.

Dohrenwend, J. C., Schell, B. A., Menges, C. M., Moring, B. C., and McKittrick, M. A., 1996, Reconnaissance photogeologic map of young (Quaternary and late Tertiary) faults in Nevada, in Singer, D. A., ed., An analysis of Nevada's metal-bearing mineral resources: Reno, Nevada, Nevada Bureau of Mines and Geology Open-File Report 96-2.

Faulds, J. E., Garside, L. J., Johnson, G. L., Muehlberg, J., and Oppliger, G. L., 2002, Geologic setting and preliminary analysis of the Desert Peak-Brady geothermal field, western Nevada: Geothermal Resources Council Transactions, v. 26, p. 491-494.

Gianella, V. P., and Callaghan, E., 1934a, The Cedar Mountains, Nevada, Earthquake of December 20, 1932: Seismological Society of America Bulletin, v. 24, p. 345-384.

-, 1934b, The earthquake of December 20, 1932, at Cedar Mountain, Nevada, and its bearing on the genesis of Basin-Range structure: Journal of Geology, v. 42, p. 1-22.

Gilbert, G. K., 1890, Lake Bonneville, U.S. Geological Survey Monograph 1, 438 p. Lachenbruch, A. H., 1978, Heat flow in the Basin and Range province and thermal effects of

tectonic extension: Pure and Applied Geophysics, v. 117, p. 34-50.

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Lachenbruch, A. H., and Sass, J. H., 1978, Models of an extending lithosphere and heat flow in the Basin and Range province, in Smith, R. B., and Eaton, G. P., eds., Cenozoic tectonics and regional geophysics of the western Cordillera: Boulder, Geological Society of america Memoir 152, p. 209-250.

Louie, J. N., 2004, Crustal thickness and seismic velocity in the Great Basin: Presentation at the Great Basin Geothermal Workshop, University of Nevada Reno, November 5, 2004.

McKenna, J. R., and Blackwell, D., 2004, Numerical modeling of transient Basin and Range extensional geothermal systems: Geothermics, v. 33, p. 457-476.

Morgan, P., and Gosnold, W. D., 1989, Heat flow and thermal regimes in the continental United States, in Pakiser, L. C., and Mooney, W. D., eds., Geophysical framework of the continental United States: Boulder, Colorado, Geological Society of America Memoir 172, p. 493-522.

Oviatt, C. G., 1991, Quaternary geology of the Black Rock Desert, Millard County, Utah, Utah Geological Survey Special Studies 73, 27 p.

Oviatt, C. G., and Nash, W. P., 1989, Late Pleistocene basaltic ash and volcanic eruptions in the Bonneville basin, Utah: Geological Society of America Bulletin, v. 101, p. 292-303.

Richards, M., and Blackwell, D., 2002, The forgotten ones, Geothermal roads less traveled in Nevada: Geothermal Resources Council Bulletin, v. 31, no. 2, p. 69-75.

Richards, M., and Bllackwell, D., 2002, A difficult search, Why Basin and Range systems are hard to find: Geothermal Resources Council Bulletin, v. 31, no. 4, p. 143-146.

Shevenell, L. A., Garside, L. J., Arehart, G. B., van Soest, M., and Kennedy, B. M., 2002, Geochemical sampling of thermal and nonthermal waters in Nevada to evaluate the potential for resource utilization: Geothermal Resources Council Transactions, v. 26, p. 501-505.

Slemmons, D. B., 1957a, Geologic setting for the Fallon-Stillwater earthquakes of 1954: Seismological Society of America Bulletin, v. 47, p. 4-9.

-, 1957b, Geological effects of the Dixie Valley-Fairview Peaks, Nevada, earthquakes of December 16, 1954: Seismological Society of America Bulletin, v. 47, p. 353-375.

Stewart, J. H., 1988, Tectonics of the Walker Lane belt, western Great Basin: Mesozoic and Cenozoic deformation in a zone of shear, in Ernst, W. G., ed., Metamorphism and cause of evolution of the western United States: Ruby Volume 7: Englewood Cliffs, New Jersey, Prentice-Hall, p. 683-713.

Thatcher, W., Foulger, G. R., Julian, B. R., Svarc, J., Quilty, E., and Bawden, G. W., 1999, Present-day deformation across the Basin and Range province, western United States: Science, v. 283, p. 1714-1718.

Trexler, D.T., Flynn, T., Koenig, B.A., and Ghusn, G., Jr., 1983, Geothermal resources of Nevada: Map produced by the National Geophysical Data Center, National Oceanic and Atmospheric Administration for the Geothermal and Hydropower Technologies Division, U.S. Department of Energy, Scale 1:500,000.

Wallace, R. E., 1984a, Fault scarps formed during the earthquakes of October 2, 1915, in Pleasant Valley, Nevada, and some tectonic implications in faulting related to the 1915 earthquakes in Pleasant Valley, Nevada, U.S. Geological Survey Professional Paper 1274-A, 33 p.

-, 1984b, Patterns and timing of late Quaternary faulting in the Great Basin province and relation to some regional tectonic features: Journal of Geophysical Research, v. 89, p. 5763-5769.

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Zehner, R., Coolbaugh, M., and Shevenell, L., 2010, Preliminary geothermal potential map and exploration activity in Nevada: Nevada Bureau of Mines and Geology Open File Report 09-10.

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Table 1. Locations of surveyed shoreline elevations in the Lahontan basin (see Fig. 1) 

All locations are in UTM NAD83 Zone 11. 

Easting  Northing  Elevation (m) 

298008  4471274  1340.4 

296823  4468940  1338.1 

292939  4464943  1338.8 

290314  4463758  1338.4 

293939  4466340  1336.9 

294189  4466599  1337.2 

294340  4466759  1338.4 

297230  4474448  1339.5 

301080  4486622  1337.0 

301959  4488008  1335.6 

327479  4514507  1335.0 

320693  4510142  1333.9 

315376  4502992  1336.1 

317137  4505144  1337.0 

316542  4504475  1337.2 

366249  4271801  1331.0 

357019  4281043  1330.2 

357072  4280861  1329.5 

357027  4280899  1329.3 

356943  4280950  1329.3 

356853  4280993  1329.6 

356692  4281054  1329.9 

356436  4281117  1330.1 

356380  4281149  1330.5 

356461  4281188  1330.8 

356612  4281254  1331.2 

356759  4281322  1331.4 

357053  4281476  1331.4 

352729  4303061  1333.4 

357648  4311691  1332.7 

361113  4312396  1331.7 

370138  4309092  1331.2 

321383  4375150  1334.9 

312573  4382183  1336.0 

311356  4382312  1335.4 

298246  4398399  1336.8 

323648  4417241  1339.1 

325559  4417784  1338.1 

334037  4414729  1339.4 

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331665  4409754  1338.9 

333630  4410741  1337.4 

341569  4404166  1337.7 

330890  4398566  1340.3 

331875  4394643  1337.9 

328762  4389613  1338.8 

326455  4386201  1337.2 

322897  4386614  1335.6 

Table 2. Locations of shoreline elevations extracted from LIDAR 

data in the Walker Lake subbasin (see Fig. 1). 

All locations are in UTM NAD83 Zone 11.

EASTING  NORTHING  LIDAR elevation  (m)

367945  4266999  1330.0

366249  4271802  1330.3

364948  4272621  1330.6

357053  4281470  1331.6

355373  4320636  1332.2

354616  4320441  1332.9

361113  4312395  1332.3

359495  4312613  1332.7

357647  4311691  1331.9

352729  4303060  1332.5

357020  4281043  1332.5

342616  4310145  1331.4

337272  4319564  1332.5

336417  4321973  1333.5

329982  4327837  1333.0

324810  4331994  1333.3

323594  4331727  1333.1

324437  4326880  1333.1

310235  4337357  1332.6

315862  4338631  1332.6

317731  4336257  1331.3

318251  4336120  1331.3

318786  4336241  1330.8

337795  4328018  1333.2

355483  4326662  1331.8

348617  4343170  1333.0

348228  4343889  1333.5

346328  4345690  1335.2

342333  4346030  1333.6

12

340260  4346278  1332.3

337245  4343991  1333.3

335597  4343537  1333.0

334790  4343505  1333.4

333927  4343991  1333.9

332255  4350069  1334.8

356333  4293069  1332.4

343566  4320441  1333.6

363714  4327227  1332.3

360112  4324843  1333.7

13

14

15

16

17