GEOLOGIC MAPPING OF THE NORTHERN CALICO MOUNTAINS, MOJAVE DESERT, CALIFORNIA

The Mojave Desert has not been mapped very well, despite being near the major population centers of Southern California. To fully understand the active tectonics of the Mojave Desert, it is important to recognize, in detail, the pre-existing geologic structures. We present a geologic map of the northern Calico Mountains, created by using a 1:12,000 scale base map and Brunton compass in the field, followed by refinement of contacts in GIS using satellite imagery overlain with USGS topography. We observed southeast-dipping albite-epidote hornfels facies Paleozoic rock units with protoliths of shale, chert, sandstone, limestone, andesite, and breccia, which appear to be deep marine slope deposits with evidence of marine landsliding. These units are intruded by plutonic rock in the NW part of the map area. Above an angular unconformity, southwest-dipping Tertiary volcanic strata were also observed, composing of mainly light-colored pyroclastic sediment with dacite lavas and lapilli tuffs of Lower Miocene age belonging to the Pickhandle Formation. The Tertiary strata are offset by normal faults that show no clear evidence of recent activity. As a result, mapping this area helped interpret alternating deep to shallow marine environments during the Paleozoic and nearby volcanic activity during the Tertiary period. Although the Calico Mountains are only a small area, our detailed map contributes to the interpretation of the tectonic and geologic story of southern California.