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| This view is looking east toward Sleeping Ute Mountain from along Utah Highway 262 (about 10 miles west of Hovenweep National Monument). This view shows the broad, flat, sweeping view of a high sagebrush desert that caps Cajon Mesa and other mesas in the region around Hovenweep National Monument in the southeast corner of Utah. Flat-lying sedimentary rocks, mostly sandstone and conglomerate of Late Cretaceous age (about 70 million years old), form the cap rock of the flat plain that makes up the mesa tops in the region. Sleeping Ute Mountain is an middle Tertiary-age volcanic intrusive complex, perhaps (if there were associated volcanoes with these intrusions, they have long since eroded away). Sleeping Ute Mountain is similar to many "laccolithic mountains" on the Colorado Plateau. A laccolith is a mass of intrusive volcanic rock that formed when molten rock (magma) migrating toward the surface becomes trapped between rock layers and pushes them apart and creates a chamber. These chambers eventually cool into solid granitic rock. Intrusive igneous activity occurred at different stages of time across the Colorado Plateau. For instance, the Henry mountains formed about 48 million years ago (MYA), The Abajos about 28 MYA, and the La Sals about 24 MYA. Based on the age of its closest neighboring volcanic mountains, Sleeping Ute Mountain probably formed sometime between about the end of the Oligocene and the beginning of the Miocene Epochs of the Tertiary Period, about 30 to 24 MYA range. |
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