The Tenmile Formation is a geologic unit in Oregon within the Eocene sedimentary sequence of the Tyee Basin. It preserves Paleogene fossils, linking it to a broad span of early Cenozoic history. Its rocks contain only limited organic matter, derived chiefly from land plants, which formed gas-prone kerogen. However, the strata remain thermally immature and have not produced significant hydrocarbons. As a result, the formation is important chiefly for what it reveals about Oregon’s ancient geologic past rather than for its potential as an energy resource.