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==