Painted Hills is one of the three units that make up the John Day Fossil Beds National Monument, located in Wheeler County, Oregon. The Painted Hills is so called for the colorful layers and banded striations that occur on its hills corresponding to various geological eras, formed when the area was an ancient river floodplain. The spectacular colors appear almost unnatural and hand-painted.

The unique colors that streak the clay rich hills and mounds were formed over 35 million years ago by volcanic ash layers deposited by ancient eruptions when the area was a river plain. Over time, the layers of ash containing different minerals compacted and solidified into the various bands of colors seen today. The black soil is lignite that was vegetative matter that grew along the floodplain. The grey coloring is mudstone, siltstone, and shale. The red and orange hues are from laterite soil that formed by floodplain deposits when the area was warm and humid.

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