Painted Hills, Oregon

The Painted Hills are a 3,132-acre unit of the John Day Fossil Beds National Monument in Wheeler County, Oregon, about 9 miles northwest of Mitchell. They began forming about 35 million years ago, when pumice and ash from volcanic eruptions in the Cascade Mountains traveled roughly 100 miles east and settled over the area; over time, water, plant growth and animal activity mixed those materials, oxidizing and compacting them into layered soil. The hills' alternating red and tan bands date to a period of cycling warm-wet and cool-dry climate roughly 34 to 28 million years ago, with the red layers formed from iron-rich laterite soils of the warmer periods and the yellow-tan layers from cooler, drier ones; black streaks mark ancient vegetation preserved as lignite, and gray tones come from mudstone and siltstone. Together the bands record the transition from the warmer Eocene epoch to the cooler, more temperate Oligocene. This entity documents the Painted Hills specifically as a geological formation.