Geology and Geomorphology of the San Bernardino Valley, Southeastern Arizona

The purpose of this project is to integrate new detailed field mapping, aerial photograph interpretation, previous research, and other available data into 1:24,000 scale geologic and geomorphic maps of the San Bernardino Valley study area (Map Pocket). Our goal is to describe the fundamental surficial and bedrock geology in a manner that can be incorporated into ecosystem and land-management research. Future work will integrate our geologic maps with soil and vegetation surveys for this portion of the Borderlands Region. The study area is in the extreme southeastern corner of Arizona in Cochise County (Figure 1). It is bounded on the south by the U.S.- Mexico border, on the east by the Arizona-New Mexico border, on the west by the Perilla and Pedregosa Mountains, and on the north-northwest by U.S. Highway 80. The main geographic features in the study area include the northern half of the San Bernardino Valley, the southern portion of the San Simon Valley, and the western side of the Peloncillo Mountains. The valleys formed during the Miocene-Pliocene period of high-angle normal faulting (the Basin and Range Disturbance) that produced alluvial basins of variable depth separated by bedrock mountains. The basins subsequently filled with volcanic and sedimentary deposits shed from the adjacent mountains and volcanic rocks erupted in the valleys. (20 pages)