landmarks. McElmo Creek and Canyon Of The Ancients National Monument form the northern terminus of the Ute Mountains and the Reservation. Geology 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. The intrusions are similar in form and rock type to those in other Colorado Plateau mountain ranges, such as the La Plata Mountains to the northeast of here, and the Rico Mountains north of Dolores, Colorado in Colorado, and the Henry Mountains, the La Sal Mountains and the Abajo Mountains, all to the west in Utah. The intrusions at these three Utah occurrences are younger at about 20 to 30 million years in age. The Ute Mountains and the similar Carrizo Mountains, nearby in Arizona, lie within a southwest extension of the Colorado Mineral Belt, but no ore deposits are known to be associated with these igneous rocks. Sedimentary units are listed below, from youngest to oldest: Formations of Cretaceous age Point Lookout Sandstone (the oldest formation of the Mesa Verde Group) Mancos Shale Dakota Sandstone Burro Canyon Formation Formations of Jurassic age Morrison Formation Bluff Sandstone (formerly called the Junction Creek Sandstone) Summerville Formation Entrada Sandstone Navajo Sandstone In some areas the soft lower unit of the Entrada weathers into characteristic rounded forms, commonly called hoodoos. The underlying Navajo weathers into rough, rounded surfaces, commonly pitted, and usually forms cliffs. See also List of Colorado mountain ranges List of Colorado mountain summits List of Colorado fourteeners List of Colorado 4000 meter prominent summits List of the most prominent summits of Colorado List of Colorado county high points References Further reading External links Mountains of Colorado Mountains of Montezuma County, Colorado North American 3000 m summits Religious places of the indigenous peoples of North America