Detail of Geologic Map Emphasizing Bedrock Formations in Contra Costa County, California. Complied by by R.W. Greyner, D.L. Jones, and E.F. Brabb.
Shell Ridge (the browns and tans) consists of the following rock units, in order of age: upper Domengine Formation (Tdu), Cierbo Formation (Tc, with sandstone/conglomerate (Tcsc) at the base), Neroly Formation (Tn), and Green Valley/Tassajara group (Tgvt).