Geologic mapping of the San Rafael Primitive Area (now the San Rafael Wilderness) by Gower and others (1966) and Vedder and others (1967) did not include all of the San Rafael Mtn. quadrangle, and the part that was mapped was done in reconnaissance fashion. To help resolve some of the structural and stratigraphic ambiguities of the earlier mapping and to complete the mapping of the quadrangle, additional field work was done during short intervals in 1980 and 1981 and from 1996 to 1998. Contacts within the belt of Franciscan rocks at the southwestern corner of the quadrangle were generalized from the detailed map by Wahl (1998).
Because extensive areas were inaccessible owing to impenetrable chaparral, observations from several helicopter overflights (1965, 1980, 1981) and interpretations from aerial photographs were used as compilation aids. Consequently, some of the depicted contacts and faults are highly inferential, particularly within the Upper Cretaceous rocks throughout the middle part of the quadrangle.