Scientific Investigations Report 2005–5288
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2005–5288
Carson Valley is in Douglas County, Nevada, south of Carson City, Nevada’s capital (fig. 2). The southern end of the valley floor extends about 3 mi into Alpine County, California. The floor of the valley is oval-shaped, about 20 mi long and 8 mi wide, and slopes from about 5,000 ft above sea level at the southern end to about 4,600 ft at the northern end. The Carson Range of the Sierra Nevada rises abruptly from the valley floor on its western side with mountain peaks ranging from 9,000 to 11,000 ft, whereas on the eastern side, the Pine Nut Mountains rise gradually to peaks ranging from 8,000 to 9,000 ft (fig. 2).
The valley floor is covered with native pasture grasses, and crop lands of primarily alfalfa, and phreatophytes such as greasewood, rabbitbrush, and big sage near the northern end of the valley. In 1997, about 38,000 acres in Douglas County were irrigated and 26,000 acres were designated as cropland (U.S. Department of Agriculture, 2004). On the western side of the valley, bitterbrush and sagebrush cover steep alluvial fans, and manzanita and ponderosa pine cover the slopes of the Carson Range. Alluvial fans and foothills on the eastern side of the valley are covered with sparse, low-lying sagebrush, whereas pinyon and juniper are more prevalent in higher altitudes of the Pine Nut Mountains.
The major towns in the valley are Minden and Gardnerville with populations in 2000 of 2,800 and 3,400, respectively (U.S. Census Bureau, 2003; fig. 2). Subdivisions of the Gardnerville Ranchos to the south and Johnson Lane and Indian Hills to the north are growing rapidly, with populations in 2000 of 11,000, 4,800, and 4,400, respectively (U.S. Census Bureau, 2003). In addition, development is increasing along the eastern and western margins of the valley, and on the valley floor on land that historically has been agricultural. Douglas County’s population, as a whole, has grown from about 28,000 in 1990 to 41,000 in 2000, an increase of 49 percent (Economic Research Service, 2003).
A major geographic feature of Carson Valley is the Carson River. The East and West Forks of the Carson River enter from the southeast and southwest corners of the valley, respectively, and flow northward to join near Genoa. The combined flow of the Carson River continues north to leave Carson Valley about 5 mi southeast of Carson City (fig. 2). Flow of the East and West Forks of the Carson River is diverted across the valley floor through a network of canals and ditches for flood irrigation of pasture grasses and crops.
For purposes of this study, a subarea of the entire Carson Valley Hydrographic Area1 was delineated (figs. 1 and 2) to include only those parts of the Hydrographic Area connected by permeable materials capable of transmitting ground water to the floor of Carson Valley. The only difference between the hydrographic area and the subarea is along the southern boundary, where the headwaters of the East and West Forks of the Carson River have been excluded. Bedrock underlies the subarea boundary where the East and West Forks of the Carson River enter the valley, and ground-water inflow is minimal through very thin fluvial sediments underlying the river channels (fig. 3). Ground-water flow across the alluvial fan west of the West Fork of the Carson River likely is parallel to the subarea boundary with minimal flow across the boundary. The subarea used for this report, as shown in figure 2, covers 253,570 acres, or about 396 mi2.
1The U.S. Geological Survey and Nevada Division of Water Resources systematically delineated formal hydrographic areas in Nevada in the late 1960s for scientific and administrative purposes (Cardinalli and others, 1968). The official hydrographic-area names, numbers, and geographic boundaries continue to be used in U.S. Geological Survey scientific reports and Nevada Division of Water Resources administrative proceedings and reports. Hydrographic-area boundaries generally coincide with drainage-area boundaries.
U.S.
Department of the Interior | U.S. Geological
Survey
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