While out wandering around a couple years back, probably on our way to or from Great Basin National Park, MOH and I ran across this rusty specimen in Spring Valley on the western flank of the southern Snake Range, not far below the ghost town of Osceola. Osceola is the center of the Osceola mining district, which largely produced placer gold. Although most reports talk about the district as though it's dead, activity is ongoing, and we often see a small recovery operation or two when we drive by on Highway 50.
This is a trommel—smaller ones can be seen here—once used as part of a placer gold recovery operation. Trommels wash the dirt and gravel and separate the coarser material from the finer material before the fines and gold are put through some kind of concentrator like a sluice box. This trommel is now only good for its scenic and historic value; here it's framing the Schell Creek Range across Spring Valley. Black Mountain is the prominent mountain and South Schell Peak can barely be seen to the west (left) in the distance [MSRmaps location].
Silva, Michael, 1986, Placer gold recovery methods: CDMG Special Report 87, 31 p.