Field maps and notes from geologic mapping by C.M. Wentworth of the Gualala structural block between Fort Ross (38º 30') and Galloway Creek (38º 52' 30''), coastal northern California, 1960-63

Field maps and notes made during field mapping by C. M. Wentworth in 1960-63 provide primary data about the structure and rocks west of the San Andreas fault in the Gualala block between Fort Ross (Fort Ross quadrangle) and Galloway Creek (Saunders Reef quadrangle). Structure (bedding attitudes, faults) and lithologies (in 5 color categories) observed in the field are plotted on the maps, together with numbered field stations. Descriptions in the notes, including collected megafossils, mudstone sampled for microfossil analysis, and sandstone sampled to determine the abundance of detrital potassium feldspar, are keyed to the maps by those field stations. These materials were a principal source in the preparation of the geologic map of the area presented in C. M. Wentworth’s 1966 study “The Upper Cretaceous and lower Tertiary rocks of the Gualala area, northern Coast Ranges, California” (Stanford University, unpublished PhD dissertation, 1966), which has served as an underlying source in numerous studies of the Gualala block and its large lateral offset along the San Andreas and San Gregorio faults.