The roughly 20 million year old John Day Foundation gently folds into colorful anticlines that ripple through the Painted Hills Unit where visitors can get a close-up look at the beautifully unique structure of the floor of this flood plain. Representing tens of millions of years of geological activity, the uniquely well preserved layers of clay, fossils and earth create one of the longest, unbroken, sequentially in-tact geological records found anywhere on the planet.
The many colored layers tell a story of ancient floods, catastrophic volcanic activity, and the rise and fall ancient forests, swamps and savannas and the many creatures and plants that called them home. The gray layers are mudstone, siltstone, and shale formed from sediments deposited on an ancient river floodplain. The black layers are thin beds of fossilized or carbonized vegetative mater (lignite) that formed in swamps on the floodplain. The red layers are ancient soil profiles (laterites) that formed on floodplain deposits. Surface weathering relatively quickly breaks down these rocks into a clay-rich surface coating that easily erodes during summer flashfloods and/or winter storms. The high clay content and rapid erosion during infrequent storms prevents plants from becoming established in the badlands areas.
"Painted Hills". Wikipedia, "http://en.wikipedia.org/wiki/Painted_Hills", Oct 20, 2010.
"John Day Fossil Beds National Monument". Wikipedia, "http://en.wikipedia.org/wiki/John_Day_Formation", Oct 20, 2010.