The Jurassic Ralston formation in the Canon City embayment crops out in the escarpment face of dipping Paleozoic and Mesozoic strata which flank the southern end of the Front Range. The exposure was traced and mapped from Canon City to Colorado Springs, Colorado. Thirty-one detailed sections were measured. Ten representative sections are included in this paper.

Four sedimentary facies occur in the Ralston formation: a conglomerate facies, a standstone facies, a gypsum-shale facies and a sand-shale facies. These are intergradational from west to east. The conglomerates are arkosic with torrential cross-laminations indicating a source in the present Wet Mountain area on the west. The sandstones are interpreted as beach deposits, and the other two facies are deposits of the Ralston sea.

Ralston sedimentation was controlled by irregularities of the surface over which the sea advanced. This surface had more than 100 feet of relief, and resulted from erosion of the Fountain and Lykins formations under arid conditions during Triassic and early and middle Jurassic time. Physiographic features of this unconformity were controlled by the upper and lower Crinkled limestones of the Lykins formation.

The base of the Ralston formation is marked by a thin, coarse, frosted, slightly arkosic quartz sand. Locally this sand contains chert ventifacts derived from the Lykins Crinkled limestones.

The contact with the overlying Morrison formation is difficult to determine exactly. Disappearance of gypsum, color change from pastels to drabber colors, great increase in carbonate content, and appearance of the welded chert beds and brown, well cemented sandstones identify the Morrison sediments.

The welded chert beds are considered to be concretionary deposits of chalcedony concentrated by ground water. Evidence indicates that locally the chalcedony has replaced aragonite twins.