Three words: Black Rock Desert.
Enough trails to keep you busy for years.
Pics from our last desert trip in 2006:
04 - NW Nevada + Black Rock Desert area July 23-27
Maps and more info:
Background Information Table
Black Rock Desert-High Rock Canyon Emigrant Trails National Conservation Area - Wikipedia, the free encyclopedia
Friends of Black Rock High Rock
Just don't go in late August unless you want to be around about 40K smelly, drug doping, anti-gun, anti-American hippies (Burning Man).