The Ute Mountains were formed by intrusion of igneous rocks at about 72 million years (Late Cretaceous), concurrent doming, and subsequent erosion. The most common type of igneous rock is porphyritic hornblende diorite, but rock types present range from gabbro to granite. Forms of intrusions include laccoliths, stocks, dikes, and sills. One dike extends north to McElmo Creek and can be examined at a roadside there. The igneous rocks intrude a sedimentary section of Jurassic and Cretaceous rocks and the youngest rocks intruded are in the Point Lookout Sandstone.