The soils found in the Horse Heaven Hills were influenced by the Missoula floods, as well as comprising wind-blown loess and ash from volcanic eruptions from Cascade volcanoes to the west considered to be part of the Palouse formation. The soils are nutrient-poor and free draining. There are small, deep canyons in the slopes of the range and other areas where the Columbia River Basalt Group is exposed. The north slope has numerous mass wasting scars. The loess contain erupted material from Mount Mazama (Crater Lake), Glacier Peak, and Mount St. Helens.