Quaternary and Upper Tertiary Sediment, Undivided

Largely river sediment; includes upper Quaternary terrace, fan, and pediment gravel composed of subanglar pebbles and cobbles of locally-derived material such as sandstone, silicified wood, and concretions and Pliocene (?) to middle (?) Quaternary clay, silt, sand, and gravel composed of rounded pebbles and cobbles of quartzite and porphyry derived from the Black Hills or Rocky Mountains; as thick as 100 meters (300 feet)