Mapping the Geology of the Southwest

By George Billingsley, Debra L. Block, Helen C. Dyer, Tracey T. Felger, Scott E. Graham, and Susan S. Priest

A variety of geologic mapping projects are underway at the Flagstaff Field Center, including geologic mapping of the Grand Canyon and Lake Mead areas, mapping destabilization of sand dunes on the Navajo Nation, and mapping climate trends in the Holocene across the southwest United States and the Gulf of California area of Mexico.

Tilted rock layers line the shores of Lake Mead.

A good example of the continuing efforts of the group is the ongoing cooperative mapping effort between the USGS and the National Park Service in the Colorado Plateau region. The goal of the cooperative U.S. Geological Survey/National Park Service (USGS/NPS) Geologic Mapping Program is to produce several 1:100,000-scale digital geologic maps of the Grand Canyon/Lake Mead region of northwestern Arizona. These maps will provide a regional geologic framework for areas not adequately mapped on the southwestern Colorado Plateau and eastern Great Basin provinces.

Geologic mapping of the Littlefield, Grand Canyon, and Mount Trumbull quadrangles in northwestern Arizona has been completed and published, and the Valle and Peach Springs quadrangles are now in review.

Geologic maps are used to address critical resource management questions such as:

• Where are the areas of highest probability for locating threatened or endangered plant and animal species?
• How might increased ground water development adjacent to the Grand Canyon affect surface and spring flows within Grand Canyon?
• What are the geologic controls for spring discharge in northwestern Arizona?

A GIS database of the southwestern Colorado Plateau lends critical support to ecological studies involving hydrologic, biologic, and environmental resources of this unique region. These maps provide baseline data to support resource management decisions on federal, state, and private lands where immediate and future environmental impact and conservation mitigation measures are needed.