Moses Coulee’s spectacular land formations reflect some of the most dramatic geological history on earth. The story began about 17 million years ago when hundreds of massive volcanic eruptions spread lava across the Columbia Plateau. Several basalt flows can be seen today in the towering walls that form Moses Coulee.
During the last Ice Age,about 15,500 to 12,500 years ago, ice dams blocking Glacial lake Missoula gave way, sending catastrophic floods across parts of Montana,Idaho, and Northeastern Washington and carving gigantic stream channels. Laden with massive loads of sand,rock and icebergs, the floodwater followed the course of the present-day Columbia River until the cordillera ice sheet blocked that flow, sending muddy torrents of water into Grand and Moses Coulees and past the Beezley hills.
Overtime the Okanogan lobe of the ice sheet continued to move south, blocking any latter floodwater’s from entering Moses Coulee and bulldozing 200-foot high accumulation of rock debris known as the Withrow Morriane. Today hanging valleys, giant ripple marks, and gravel bars help visitors see how catastrophic flooding once shaped this broad deep Coulee.
Tribes of semi-nomadic people began hunting,fishing,and gathering plants within the Moses Coulee Beezley Hills region more then 11,000 years ago.