Hagerman Fossil Beds National Monument - Natural Features

Hagerman Valley is in the central Snake River Plain region of the eastern portion of the Columbia Plateau. The Snake River, which flows west, then north, through the valley, forms the eastern boundary of the Monument. On the Monument side of the river, the valley wall rises steeply and abruptly about 550 feet above the river. Much of this steep terrain forms badland-type topography characterized by bluffs, landscape scarps, and hummocky (hilly) deposits. The steep slopes consist of Glenns Ferry Formation bluffs. The bluffs, known locally as the Hagerman Cliffs, are composed primarily of unconsolidated lake, floodplain, stream deposits, volcanic ash, and thin basalt flows deposited during the Pliocene and Pleistocene eras about 3.5 million years ago.

There are many drainages in the Monument, but no perennial streams other than the Snake River. Two washes dominate the bluffs. One is Fossil Gulch, which cuts through important fossil beds. The second larger wash is Peters Gulch, an intermittent stream at the southeast corner of the monument, which also dissects several fossil beds before entering the river.