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Map of recently active traces of the Rodgers Creek Fault, Sonoma County, California

July 6, 2018

The accompanying map and digital data identify recently active strands of the Rodgers Creek Fault in Sonoma County, California, interpreted primarily from the geomorphic expression of recent faulting on aerial photography and hillshade imagery derived from airborne lidar data. A recently active fault strand is defined here as having evidence consistent with slip during the Holocene epoch (approximately the past 11,700 years). The purpose of the map is to update the fundamental fault dataset for characterizing surface-rupture hazard, siting slip-rate and paleoseismic studies, and studying the geometry and evolution of slip. To serve a range of users, the map is presented in several formats: as an image map, as a digital database for use within GIS, and as a KML file for visualizing the fault using virtual globe software.

Important outcomes of this mapping revision include the following: (1) a northward 17-km increase in the known length of Holocene-active faulting to include most of the Healdsburg Fault, a structural continuation of the Rodgers Creek Fault northwest of a bend in the fault at Santa Rosa; (2) first-time identification of fault strands across the Santa Rosa Creek floodplain in central Santa Rosa; (3) increases in the known width and complexity of faulting; and (4) identification of fault splays that project toward the Bennett Valley-Maacama Fault system to the east and toward a recently mapped active extension of the Hayward Fault to the south beneath San Pablo Bay.