Regional stratigraphic units and structural features of the Lake Mead region are presented as a 1:250,000 scale map, and as a Geographic Information System database. The map, which was compiled from existing geologic maps of various scales, depicts geologic units, bedding and foliation attitudes, faults and folds. Units and structural features were generalized to highlight the regional stratigraphic and tectonic aspects of the geology of the Lake Mead region. This map was prepared in support of the papers presented in this volume, Special Paper 463, as well as to facilitate future investigations in the region. Stratigraphic units exposed within the area record 1800 million years of geologic history and include Proterozoic crystalline rocks, Paleozoic and Mesozoic sedimentary rocks, Mesozoic plutonic rocks, Cenozoic volcanic and intrusive rocks, sedimentary rocks and surficial deposits. Following passive margin sedimentation in the Paleozoic and Mesozoic, late Mesozoic (Sevier) thrusting and Late Cretaceous and early Tertiary compression produced major folding, reverse faulting, and thrust faulting in the Basin and Range, and resulted in regional uplift and monoclinal folding in the Colorado Plateau. Cenozoic extensional deformation, accompanied by sedimentation and volcanism, resulted in large-magnitude high- and low-angle normal faulting and strike-slip faulting in the Basin and Range; on the Colorado Plateau, extension produced north-trending high-angle normal faults. The latest history includes integration of the Colorado River system, dissection, development of alluvial fans, extensive pediment surfaces, and young faulting.

Abstract Standing astride the Utah-Arizona border with bronzed shafts of sandstone, the buttes and pinnacles of Monument Valley rise above the high desert floor of the central Colorado Plateau. The valley is tucked into the apex of the southern end of the Monument Upwarp, a large asymmetrical anticline bounded on its southern and eastern margins by the Comb Ridge monocline (Fig. 1). As recently as 35 years ago, no paved roads served the remote region, today three U.S. highways (U.S. 160 running east-west, and U.S. 163 and U.S. 191 running north-south), provide access to the region. But the best way to see Monument Valley is via the back roads that provide access to some spectacular backcountry. Monument Valley is located within the Navajo Indian Reservation. Travel on paved and main dirt roads is generally unrestricted. However, travel in some areas is restricted and a permit is required for rock collecting or extensive geological study. Inquiries should be addressed Navajo Nation, Window Rock, Arizona 86515. Monument Valley and vicinity is covered by geologic maps of various scales 1:62,500 (Witkind and Thaden, 1963), 1:96,000 (Baker, 1936), 1:250,000 (U.S.G.S. Iseries, 345, 629, 744, 1003), and 1:500,000(Geological Maps of Utah and Arizona). Witkind and Thaden (1963) have provided the most comprehensive geological report of the region.