The Marysvale volcanic field in southwestern Utah is a vast volcanic region at the boundary of the Colorado Plateau and the Great Basin, made up of many landforms rather than a single mountain. One of the largest volcanic fields in the western United States, it preserves a long record of activity through stratovolcanoes, calderas, lava domes, and cinder cones. Most of its igneous rocks formed in a middle Cenozoic calc-alkaline sequence about 32 to 22 million years ago, while a smaller later phase of mainly basalt and rhyolite continued from about 23 million years ago into the Holocene. This history makes it important for understanding changing volcanism in the interior West.