Monument Ridge, the table-like mountain on the horizon, took its name from rock monuments built years ago by sheepherders to mark the boundaries of their grazing lands, and two can be seen on the slopes of the far ridge. In its rush to join the Imnaha River, Horse Creek drops nearly 5000 feet in the 22 mile-long canyon below. Tributary streams of the Snake River have caused this high tableland to be cut by deep canyons.