Signature Features of the Colorado Plateau
February 20, 2008
The Colorado Plateau occupies a large section of northern Arizona and eastern Utah, along with portions of New Mexico and Colorado. It lies at elevations ranging from about 5,000 to 12,000 ft. (1.5 to 4 km) -- this is the principal upper catchment area of the Colorado River. Bryce Canyon, Zion and the Grand Canyon National Parks provide impressive stratigraphic exposures. The image above, taken on the Navajo Indian Reservation just east of Kayenta, Arizona, shows several characteristics of this unique landscape.
The high plateau is generally underlain by flat-lying sedimentary rocks of Mesozoic age, as seen in the distance. Many east-dipping monoclines have resulted from the force of the North American plate colliding with the Pacific Plate. Comb Ridge monocline is seen here dipping toward the camera -- it is composed of Jurassic Navajo Sandstone. The pink sand is derived from sandstone layers that contain oxidized iron.
On top of the sedimentary sequence are numerous more recent igneous mountain masses such as the volcanic San Francisco Peaks of Arizona and the Henry Mountains batholith (magma intrusion) of Utah. Agatha Peak, in the middle-distance, is the core of a volcano that spread its lava over an unknown area along with dozens of similar nearby volcanic necks. Photo taken in March of 2007.