The formation, of late Oligocene(?)-early Miocene(?) age, is a fluviatile-lacustrine unit which at depth contains hydrocarbons. Criteria recognized in thin section which identify the formation as fluviatile nonmarine are: textural immaturity, poorly sorted quartz grains, bimodal particle-size distributions, low grain roundness and sphericity, moderately abundant flat-grain alignments, absence of unabraided marine fossils, presence of wood, leaves, bone fragments and fresh-water mollusks, scarcity of glauconite, absence of authigenic primary and secondary cements or grains of calcite, dolomite, or siderite. Volcanic detritus is the major component of the formation. Quartz, chert, and heavy minerals derived from metamorphic, plutonic and sedimentary terranes form the remainder. Data on feldspars, matrices and diagenesis are incomplete.