Horse Heaven Hills is a long ridge of rolling uplands in eastern Washington between the Simcoe Mountains and Wallula Gap, bordered in part by the Columbia River and the Yakima River valley. Formed by compression in the Columbia River Basalt Group and later reshaped by Ice Age floods, it includes features such as Lake Lewis deposits and glacial erratics. Its hot, dry, mostly treeless landscape long served Native peoples as hunting ground and a territorial boundary. Recorded by the Lewis and Clark Expedition in 1805, the region later became important for dryland wheat farming, irrigation agriculture, and, more recently, vineyards and wineries recognized through the Horse Heaven Hills AVA.