Canyonlands National Park and Monument Valley, Eastern and Southern Utah

Abstract

The eastern and southern parts of the state of Utah, southwest USA, contain some of the world’s most spectacular desert landforms. The principal feature of the Canyonlands National Park is the occurrence of deep, near-vertical walled, sinuous canyons. The mesas and rock monoliths at Monument Valley are universally known as they have been shown in many films and television series. The dominant physiographic and geologic feature of the region is the Colorado Plateau, an extensive, high-altitude hinterland that extends into Arizona, Colorado, and New Mexico. The plateau is underlain by mostly Upper Palaeozoic-Mesozoic sedimentary rocks which encompass a broad period of the Earth’s history. Regional uplift during the Late Cenozoic initiated a period of intensive erosion and the paucity of younger strata is a characteristic feature. Moreover, the Palaeozoic-Mesozoic strata reveal only modest levels of deformation and are mostly flat-lying. The arid or semi-arid environment of large parts of the southwestern USA is essential for preservation of canyons, mesas (flat-topped hills), and rock monoliths which would probably be destroyed in wetter climates. Canyons develop where the uplifted, flat-lying strata is being rapidly incised by major rivers that experience seasonal flooding. Annual flooding of the Colorado River system in eastern and southern Utah is enhanced by snow melt derived from the Rocky Mountains. The deeply-incised nature of canyons, together with the verticality of the rock monoliths, is related to differential erosion of the sedimentary strata. The steepest cliff sections in the canyon walls and monoliths, as well as the capping to mesas, typically consist of resistant sandstone formations. The softer impure sandstone, mudstone, and shale are more readily eroded. The canyons of the Colorado River and Green River at the Canyonlands National Park expose a succession of sedimentary strata which extend from the Upper Carboniferous, through the Permian-Triassic, and into the Lower Jurassic. The intercalation of resistant sandstone beds with more readily eroded impure sandstone, mudstone, and shale is particularly well exposed at Dead Horse Point. The Dead Horse State Park forms an adjunct to the national park. The Shafer Trail provides vehicle access to a prominent bench located low down in the canyon. The bench is associated with the White Rim Sandstone (Lower Permian), an anomalously resistant stratum that can be delineated over large parts of the national park. The monoliths at the Navajo Tribal Park, Monument Valley, include buttes, pinnacles, and spires with names such as Rain God Mesa, West and East Mitten Butte, and Totem Pole. Most of the steepest cliff sections consist of the resistant De Chelly Sandstone (Lower Permian). This formation is the lateral-equivalent of the White Rim Sandstone. The mesas together with some of the higher monoliths are capped by the Shinarump Conglomerate. This Upper Triassic formation forms a resistant capping over large parts of southern Utah and northern Arizona.

Photographs not otherwise referenced are by the author