The ultimate source of arsenic probably is volcanic rocks and sediment derived from volcanic rocks. In surface waters within the NVBR Study Unit, uranium concentrations were high in Las Vegas Valley and Carson Desert. Shallow ground-water seepage into Las Vegas Wash is the most likely source. Most of this released uranium is quickly removed from the water by attachment to fracture surfaces and fine-grained sediment and organic material. The resulting uranium-rich sediment grains and organic material have been transported to downstream valleys.
Granitic rocks have uranium concentrations that are high relative to most rocks.
Another possible source of mercury in Steamboat Creek was silver and gold ore processing in Washoe Valley during the late 1800s. Surface and ground water are affected by these processes directly and indirectly. Truckee River downstream from Lake Tahoe September 1992. Photograph by Ronald P. Collins, U.S. Geological Survey. Truckee River upstream from Pyramid Lake, September 1994.