Wellington soils have SL or SCL Bt horizons. Colthorp soils are on basalt plains, terraces and on plug domes and lava flow lobes on lava plains and shield volcanoes. Elevations range from 2,600 to 4,700 feet. Slopes are 0 to 20 percent. The soils formed in silty alluvium from loess and weathered volcanic ash overlying basalt.
Winters are cool and moist and summers are hot and dry.
Average annual precipitation is 8 to 12 inches. The frost free season is about 100 to 160 days. These are the Chilcott , Elijah , McCain , Power , Purdam , and Sebree soils. Chilcott soils are deeper than 20 inches to a duripan and contain more than 35 percent clay in the textural control section. Elijah and Purdam soils are deeper than 20 inches to a duripan.