Scoured by the Glacial Lake Missoula floods, soil on the hill has only been formed over the last 12,000 years. Although some soil has been formed by weathering rocks, most is composed of volcanic ash from Mt. Mazama (6,500 years ago) and soil blown in by the wind. The upper layer is being formed by decaying plants and animals. Soil depth on Tubbs Hill rarely exceeds 5 inches. Since plant roots stabilize soil, areas with little vegetation are prone to erosion. Please help reduce erosion by remaining on trails.
