Touchet Formation, Geological formation in south-central Washington, United States.
The Touchet Formation is a geological formation in south-central Washington displaying stacked layers of sediment up to 330 feet (100 meters) thick. The visible deposits show alternating bands of coarser and finer materials created by repeated sedimentation events.
Richard Foster Flint first documented this formation in 1938 at the confluence of Touchet River and Walla Walla River. The layers formed through repeated flooding events that occurred thousands of years ago.
The formation provides educational opportunities for geology students to study sedimentary processes and flooding patterns through field observations and research activities.
The formation can be viewed at multiple locations including highway cuts and river valley areas west of Walla Walla. Visitors should prepare for uneven terrain and bring appropriate clothing for outdoor conditions.
The layers contain between 40 and 62 separate rhythmites, each marking an individual flood event from an ancient glacial lake. Each thin band tells the story of a single prehistoric flood episode.
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