Ash and pumice from the ancestral Cascades and local volcanoes buried this area layer by layer, depositing the colorful layers before you thirty-three million years ago. To connect the broken-looking pieces across the hills, similar color, thickness, and sequence can be traced through the layers, though underground forces later lifted and faulted the strata and interrupted their symmetry. Soil formation processes affected each layer differently, and clays formed and were deeply buried until they turned to stone. The red in the Painted Hills comes from rusty iron minerals oxidized by long exposure, the golden layers show a mix of oxidized magnesium and iron in metamorphic claystone minerals, and black hash marks are rich in manganese. Each color reflects a different geologic process in a valley shaped by geologic change, with erosion from rain as the latest sculptor.