Named for Marsh Creek in vicinity of Mount Diablo, northern CA. Name first "provisionally" used by Durham and Colburn (1963). Type section designated on north flank of Mount Diablo (base of section, sec.29 T1N R1E and top of section, near old Marsh ranch house (NW corner, sec.34 T1N R1E) Contra Costa Co, CA. Best exposures are in Marsh Creek bottom. Unit completely encircles Mount Diablo and extends to southeast along axis of Diablo Range beyond area of report. Consists of sequence of alternating sandstones and mudstone. Composite thickness is estimated to be over 30,000 ft. Base is not exposed. Lower boundary is drawn at fault contact with Franciscan rocks that make up core of Mount Diablo. Conformably underlies "Deer Valley" formation (new) on northeast side of Mount Diablo. On northwest side underlies with angular unconformity, the "Domengine". In Riggs Canyon underlies with angular unconformity Meganos formation. In Black Hills conformably underlies "San Pablo" formation. Abundant mega- and micro-fossils indicate age is Late Jurassic to Late Cretaceous.

Source: GNU records (USGS DDS-6; Menlo GNULEX).