CONTRIBUTIONS TO THE SIERRA NEVADA DIGITAL EARTH SCIENCE ATLAS: DIGITAL GEOLOGIC MAP COMPILATION OF CRETACEOUS TO QUATERNARY UNITS IN THE SIERRA NEVADA

As part of the Sierra Nevada Digital Earth Science Atlas project (SNDESA), the California Geological Survey (CGS) has compiled geologic mapping of Cretaceous to Quaternary “overlap assemblage” geologic units in a digital database at 1:400,000 scale. This portion of the compilation effort includes all sedimentary and volcanic deposits from the Cretaceous Great Valley Group and younger, excepting glacial and landslide deposits which were compiled separately. Best-available mapping was utilized, with publication dates ranging from 1958 to 2020, and map scales ranging from 1:24,000 to 1:250,000. More than 300 map units were compiled from these sources and simplified to about 30 map units representing key geologic elements appropriate for representation at 1:400,000 scale. Available literature was utilized to refine age designations, unit descriptions, and genetic interpretations where possible.

The resulting compilation of these map units record: multiple episodes of Cretaceous to Miocene marine sedimentation along the western margin of the range; two periods of Eocene to Miocene deposition of fluvial sediments and pyroclastic flows in West-trending range-crossing channels draining the Nevadaplano, and associated deltaic-estuarine-marine sedimentation at the fluvial-marine interface; Miocene to Pliocene volcanism of the Ancestral Cascade arc and associated sedimentation; multiple episodes of Miocene to Quaternary volcanism of extensional and other genesis; Quaternary volcanism of the modern Cascade arc; and, Pliocene to Quaternary sedimentation in fluvial systems, lakes, and other environments.

A secondary objective of this effort is to produce the largest-scale and most current range-wide map compilation of these units. It is hoped that this compilation will be of use as a general reference to the public, a ready source of geologic information for examination of range-wide patterns, and as a resource for future studies of Sierra Nevada geology.