Igneous activity similar to that in the Oligocene continues until approximately 15 million years ago. Basalt flows and volcanic cones form in southwestern Utah. Regional uplift rejuvenates major river systems in the Rocky Mountains and the Colorado Plateau. The carving of the canyonlands begins. The igneous rocks that form the Henry, La Sal, and Abajo Mountains in southern Utah begin to intrude.
Igneous activity produces intrusive rocks in northern Utah and volcanos in southwestern Utah.
The majority of Utah's copper is probably associated with an Oligocene-age intrusion in the Bingham mining district, west of Salt Lake City. Lake Uinta, part of a larger Green River Lake system in Wyoming and Colorado, forms in northeastern Utah. The lake gradually contracts and is replaced by a river system. In the Uinta Basin thousands of feet of sediment are deposited. Granitic intrusions and volcanic flows occur in northwestern Utah during the late Eocene.