Half Dome, California, USA
U.S. Geological Survey photo (fair use policy)
Half Dome is the most famous landmark in Yosemite Valley, California. It's very likely that Half Dome never had another half, at least not one as well formed as this. The flat face overlooks Yosemite Valley, whose U-shaped cross section is attributed to glacial action. The dome itself reflects the general shape of an intrusion of granodiorite deep underground. As the intrusion became exposed by erosion, the change in pressure caused the rock to crack apart in thin shells, which fall off the sides and leave the mountain clean. The process is called exfoliation, and Half Dome is a classic exfoliation dome.