Scientific Investigations Report 2006–5099
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5099
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Great Basin National Park, in east-central Nevada (fig. 1), is home to an abundance of natural resources and scenic attractions. The park encompasses Lehman Caves; Wheeler Peak, the second highest peak in Nevada at 13,063 ft; many glacial features, such as a remnant glacier, a rock glacier, cirques, and tarns; a bristlecone forest; subalpine lakes; as well as abundant wildlife (National Park Service, 1991, 2002; Miller and others, 1995a). Water from streams, springs, and seeps within Great Basin National Park is an important resource that maintains the diverse biological communities, enhances the abundance of geologic features, and provides for park operations.
The water resources of sparsely populated valleys in eastern Nevada and western Utah have received attention as potential sources of supply because of the increased demand for water in distant urban centers, in particular Las Vegas, Nevada. Several water-rights applications, including those filed by Las Vegas Valley Water District and Vidler Water Company, a private water-development firm, currently (2006) are pending before the Nevada State Engineer for large-scale ground-water withdrawals from Spring and Snake Valleys adjacent to the park. Streams, springs, and seeps in the park potentially could be affected because of the close proximity to the pending withdrawals. Any decreases in flow could adversely affect water-dependent biological and geological resources within the park as well as the park’s water supply. The National Park Service (NPS) needs information on how the proposed withdrawals might affect water resources important to the park. The U.S. Geological Survey (USGS) is working, in cooperation with the NPS, to assess the park’s surface-water resources and determine where the resources are most susceptible to ground-water withdrawals. The information presented in this report will assist NPS in managing and protecting the natural resources that may be affected by proposed ground-water withdrawals outside of the park’s boundary.
The purpose of this report is to document the results of a study to characterize surface-water resources in the Great Basin National Park area, and to evaluate the susceptibility of those resources to ground-water withdrawals in adjacent valleys. Characterization of surface-water resources included quantifying the discharge of streams and springs within the study area, and assessing the natural variability of their flow. For the purpose of this report, the study area is defined as that part of the southern Snake Range south of Highway 50 that includes the Great Basin National Park, Humboldt National Forest, and adjacent areas that encompass the alluvial slopes and upper parts of the valley floor. Alluvial slope is used herein to describe the piedmont alluvial plain that has formed around the periphery of the southern Snake Range.
A streamflow network was developed to monitor the discharge of principal streams and springs in the study area. A series of synoptic streamflow measurements were made along six of the drainage basins during snowmelt runoff in the spring and summer, and during low flow in the autumn. Streamflow data were compared with precipitation data to characterize natural fluctuations in stream discharge. Surface-water resources in the study area that likely and potentially are susceptible to ground-water withdrawals in the adjacent valleys were determined from relations between changes in stream discharge and geologic units along each stream.
Great Basin National Park is in east-central Nevada near the border of Utah. The park covers more than 120 mi2 (National Park Service, 2002), generally encompassing much of the southern Snake Range (fig. 1). The southern Snake Range is a north-south trending mountain range bounded on the east and west by Snake and Spring Valleys, respectively. Great Basin National Park is within the Great Basin hydrographic province where streams drain internally; the Great Basin hydrographic province is part of the larger Basin and Range physiographic province (Fenneman, 1931) where great differences in altitude between mountain ranges and adjacent valleys are typical. Wheeler Peak, at 13,063 ft, is the highest peak in the southern Snake Range, and the second highest peak in Nevada (Miller and others, 1995a; National Park Service, 2002). Altitudes in the valleys adjacent to the range are about 5,000 ft in Snake Valley to the east, and 5,800 ft in Spring Valley to the west.
The large variation in climate at and near Great Basin National Park is typical of northern and central Nevada (Houghton and others, 1975). This variation creates a range of habitat zones throughout the park as precipitation, temperature, and vegetation differ with altitude (National Park Service, 2002). The climate ranges from a midlatitude steppe in the valleys adjacent to the park to a humid continental climate at the highest altitudes in the park (Houghton and others, 1975). The midlatitude steppe is characterized as semiarid with cold winters and hot summers, whereas the humid continental climate is characterized by heavy precipitation, cold winters, and mild summers (Houghton and others, 1975). Sagebrush (Artemisia L.) is the dominant vegetation in the midlatitude steppe, and pinyon (Pinus monophylla)-juniper (Juniperus L.) woodlands and aspen (Populus tremuloides)-coniferous forests prevail in the mountains, except for the highest altitudes where alpine tundra is dominant (U.S. Department of the Interior, 1992; Orndorff and others, 2001).
Precipitation at the park is from three types of storms (Houghton and others, 1975). Storms that form as low-pressure systems in the Pacific move across the Sierra Nevada and Cascade Range. Although all of Nevada is in the rain shadow of these mountains, heavy precipitation from these storms can occur. Continental storms, or Great Basin lows, as referred to by Houghton and others (1975), occur when low-pressure systems build over Nevada and Utah. The lows build along cold fronts influenced by polar-air masses brought southward by northerly winds. These storms are most common from April to June, but can produce heavy snowfall during the winter. Convective thunderstorms from moist air that moves into the region from the Gulf of California and the Gulf of Mexico during late summer can produce intense rainfall.
All three types of storms are reflected in the mean monthly precipitation graph shown in figure 2. Mean monthly precipitation and air-temperature data for 1971–2000 are from the National Weather Service (NWS) weather station operated at the Lehman Caves Visitor Center (fig. 1; National Oceanic and Atmospheric Administration, 2002). Mean annual precipitation at the visitor center during this period was 13.61 in. Mean monthly precipitation ranged from 0.7 in. in December to 1.7 in. in September (fig. 2). Precipitation generally was greatest in late winter (February–March) from Pacific storms, in May from continental storms, and late summer to early autumn (August–October) from convective thunderstorms.
Mean monthly air temperatures at the Lehman Caves Visitor Center from 1971–2000 are shown in figure 2. The mean annual air temperature was 8.6°C. Mean monthly temperatures ranged from a low of -1.8°C in January to a high of 21.8°C in July. Mean monthly temperatures were below freezing from December through February and most precipitation during this period accumulated as snow.
Snow accumulates at high altitudes generally beginning in November and continues through March. Snowmelt usually begins in March and continues into summer, with snow at the highest altitudes melting last. Snow can remain in some protected, high-altitude areas throughout the year. As a result, a perennial ice field has formed in the cirque on the north side of Wheeler Peak (fig. 1).
The southern Snake Range is part of a metamorphic core complex that was uplifted and exposed by erosion during extensional faulting that began in the Tertiary (Miller and others, 1999). The metamorphic core complex exposed Cretaceous granites, and metamorphosed Proterozoic and Paleozoic sedimentary rocks in the northern half of the range (McGrew and others, 1995; Miller and others, 1995a). Younger, Paleozoic (Middle Cambrian through Devonian) sedimentary rocks overlie the core complex in the southern half of the range; underlying these rocks is a major, gently east-dipping fault surface, known as the southern Snake Range décollement (pl. 1, table 1; McGrew and others, 1995). As a result of extensional faulting, the southern Snake Range is tilted eastward, creating a steep slope on the west side and a shallow slope on the east side (Orndorff and others, 2001). Uplift has been much greater to the north, where the core complex is exposed (pl. 1). Detritus eroded from the uplifted mountains has partially filled the surrounding valleys. This process of erosion and fill continues today.
Geologic units throughout the study area consist of sedimentary, metamorphic, and igneous rocks ranging in age from Late Proterozoic to Quaternary (table 1). The older undifferentiated rocks of Late Proterozoic and Early Cambrian Age mostly are quartzite, argillite, and shale that correspond to the McCoy Creek Group (Misch and Hazzard, 1962; Hose and Blake, 1976; Miller and others, 1995a), Prospect Mountain Quartzite, and Pioche Shale (table 1; Misch and Hazzard, 1962; Whitebread, 1969; Hose and Blake, 1976; McGrew and others, 1995; Miller and others, 1995a, 1995b). These rocks are found mostly in the lower plate of the southern Snake Range décollement. The McCoy Creek Group generally consists of weakly metamorphosed quartzites, argillites, and siltstones with a combined thickness of about 3,600 ft (Misch and Hazzard, 1962; Miller and others, 1995a). The quartzites are fine to coarse grained, thinly bedded to massive, cliff-forming units; whereas, the very fine-grained argillites and siltstones are slope-forming units (Misch and Hazzard, 1962; Miller and others, 1995a). The Prospect Mountain Quartzite is fine to coarse grained, very light gray to red-purplish gray, crossbedded, and finely jointed (Misch and Hazzard, 1962; Whitebread, 1969; McGrew and others, 1995; Miller and others, 1995a, 1995b). The unit is at most 5,000 ft thick, and forms cliffs and talus-covered slopes (McGrew and others, 1995). The Pioche Shale is a thin bedded, fine-grained, calcareous quartzite with some beds and lenses of sandy limestone, to a light-olive-gray to dark-greenish-gray siltstone, and sandy siltstone that is at most 450 ft thick (Whitebread, 1969; McGrew and others, 1995; Miller and others, 1995a).
All rock units within the older undifferentiated rocks of Late Proterozoic and Early Cambrian Age generally impede and restrict ground-water flow (Plume, 1996, p. B-29; Harrill and Prudic, 1998, p. A20). Such rocks store and transmit only small quantities of water along fractures and joints unless highly fractured (table 1). Because of the fine joint pattern along remnant bedding planes, the Prospect Mountain Quartzite may transmit more ground-water flow relative to the more massive quartzites of the McCoy Creek Group.
Undifferentiated sedimentary rocks of Middle Cambrian Age consist of Pole Canyon Limestone, Lincoln Peak Formation, and Johns Wash Limestone (table 1; Hose and Blake, 1976). These rocks are found in the lower and upper plates of the southern Snake Range décollement. The Pole Canyon Limestone is a thin-bedded to massive unit consisting of alternating members of dark-gray limestone with white to light-gray, cliff-forming limestone (Drewes and Palmer, 1957; Whitebread, 1969). The unit is about 1,800 ft thick (Whitebread, 1969). The Lincoln Peak Formation is a fine to coarsely crystalline to clastic, medium-dark gray, very thin-bedded limestone and shaly limestone (Drewes and Palmer, 1957; Whitebread, 1969). The unit is about 4,000–4,500 ft thick and is a slope former (Whitebread, 1969; McGrew and others, 1995). The Johns Wash Limestone is a light to dark gray, thin-bedded to massive, cliff-forming unit that is at most 285 ft thick (Drewes and Palmer, 1957; Whitebread, 1969; McGrew and others, 1995).
The Pole Canyon Limestone, where highly fractured, or where dissolution along fractures and bedding planes has increased porosity, can transmit large quantities of water. Lehman Caves and the Baker Creek cave system, the largest cave system discovered in Nevada (Bridgemon, 1965), are formed in this limestone. Caves have formed not only in the Pole Canyon Limestone, but also in every exposed carbonate unit throughout the park (Matthew Reece, National Park Service, Great Basin National Park, written commun., 2005).
The younger undifferentiated rocks consist mostly of limestone, shale, quartzite, and dolomite of Devonian to Late Cambrian Age. These rocks include the Corset Spring and Dunderberg Shales; Notch Peak Limestone; the Pogonip Group, undifferentiated; Eureka Quartzite; Laketown and Fish Haven Dolomites, undivided; Sevy Dolomite; and the Guilmette Formation (table 1; Hose and Blake, 1976), and generally are found in the upper plate of the southern Snake Range décollement. The limestones generally are very fine grained to coarsely clastic, medium to dark gray, thin bedded to massive with some chert nodules, lenses, and shale. The rocks are slope to cliff formers and range in thickness from 400 to 1,800 ft (Drewes and Palmer, 1957; Whitebread, 1969; McGrew and others, 1995; Miller and others, 1995a, 1995b). The shales are fissile, yellowish brown to olive gray with some limestone lenses and nodules, and are at most 470 ft thick (Drewes and Palmer, 1957; Whitebread, 1969; McGrew and others, 1995). The quartzite consists of a very light gray, fine to medium grained, thick bedded, cliff-forming unit that is at most 440 ft thick (Whitebread, 1969; McGrew and others, 1995). The dolomites are light to dark gray, microcrystalline to very finely crystalline with poorly developed or thin to medium bedding, and are at most 1,500 ft thick (Whitebread, 1969; McGrew and others, 1995; Miller and others, 1995a).
The limestones and dolomites of the younger undifferentiated rocks are discontinuous because of numerous faults, and also are fractured and thus generally transmit large quantities of ground water. Spring Creek discharges from the Laketown and Fish Haven Dolomites, which have poorly developed beds obscured by fractures (table 1; Whitebread, 1969). The Eureka Quartzite, however, generally transmits only small quantities of ground water and typically is a barrier to ground-water flow (Winograd and Thordarson, 1975, p. C74).
The intrusive rocks range from Jurassic to Tertiary Age, and consist of quartz monzonite, granodiorite (Lee and others, 1968; Hose and Blake, 1976, p. 26; Whitebread, 1969), and aplites and pegmatites (table 1; Lee and others, 1970; Lee and others, 1986; McGrew and others, 1995; Miller and others, 1995a). These rocks generally act as confining units but may transmit small quantities of ground water where fractured or weathered.
The Tertiary rocks consist of volcanic and younger sedimentary rocks including alluvial fan deposits, sand, gravel, and conglomerates (Whitebread, 1969; Hose and Blake, 1976; Miller and others, 1995a, 1995b). Displaced masses or landslide blocks of Paleozoic rocks are found locally (Whitebread, 1969; McGrew and others, 1995). The Tertiary rocks range from slightly to well consolidated or cemented. The well-consolidated or cemented rocks typically act as confining units.
The alluvial and glacial deposits generally consist of unconsolidated clay, silt, sand, and gravel that have been eroded from the southern Snake Range and adjacent mountains. The younger Quaternary deposits typically are unconsolidated, whereas the older Quaternary and Tertiary deposits range from unconsolidated to consolidated (McGrew and others, 1995; Miller and others, 1995a, 1995b). The glacial deposits generally are within the southern Snake Range and consist mostly of ground moraine from two glacial stages (Whitebread, 1969; Miller and others, 1995a). Alluvial and glacial deposits can range from poorly sorted to well-sorted (Thornbury, 1969). As a result, the water-storing and transmitting properties of these deposits can vary greatly, and are dependent on the material size, sorting, and cementation. Alluvial deposits that partly fill the basins in Snake and Spring Valleys are included in the basin-fill aquifers of the Great Basin (Plume, 1996, p. B14). The basin-fill aquifers are the most utilized aquifers in the Great Basin (Harrill and Prudic, 1998, p. A7).
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