Frenchman Mountain rises about 2,000 feet above the valleys east of Las Vegas and stands out as a sharp landmark along the city's edge. Its greatest significance is geological: faulting lifted and tilted rock layers, and erosion shaped the mountain, exposing a striking example of the Great Unconformity, where Paleozoic Tapeats Sandstone rests atop far older Paleoproterozoic Vishnu Schist. That schist, formed about two billion years ago, is among the oldest rock on the North American continent. Nearby features such as Rainbow Gardens, Lava Butte, and the Frenchman Mountain Fault add scientific importance, while the fault also poses a notable earthquake hazard for Clark County.