This dataset consists of digital geologic data for the Dry Valley Hydrographic area, Nevada and California. It was compiled from individual 1:250,000-scale geologic data for Washoe County, Nevada, 1:62,500-scale geologic data for the Chilcoot and Doyle 15' quadrangles in California and the results of field mapping within the study area in 2004. A revised geologic map was needed in the study area because the available published maps have large discrepancies between the reported geologic units along the state line. The 2004 field mapping was confined to an area approximately 2000 feet east and west of the California/Nevada state line and about 1.5 miles north and south of Dry Valley Creek. No attempt was made to resolve discrepancies between the published maps in the area outside of the designated mapping area. The discrepancies between geologic units in the previously published maps directly affect flow calculations used in the water budget for Dry Valley. The geologic unit involved in the greatest discrepancy is a non-welded rhyolitic tuff. Contacts between this unit and Quaternary basin-fill sediments were refined based on field mapping and sampling; and aerial photography. During mapping, low hills along the southern side of the valley floor 0.5 to 1.3 miles east of the state line mapped as Quaternary alluvium by previous efforts were recognized as non-welded rhyolitic tuff. In the locations described above, the non-welded tuff is distinguished by a lag deposit of yellow and red rhyolitic gravel at land surface. In the sub-surface, reached by digging, the tuff is weathered to a dense clay. Outcrops of the tuff with faint bedding planes were located in washes. Sample points, outcrops, and contacts between the tuff and unconsolidated sediments were located in the field using a handheld Garmin GPS unit (model GPS76).