Stratigraphy of the Dakota Sandstone and intertongued Mancos Shale along the southern flank of the San Juan Basin, west-central New Mexico
— Donald E. Owen and Owen, Donald E., Jr.

The bold cliff exposures of the Dakota Sandstone and intertongued offshore marine Mancos Shale between the Church Rock area on the west and the Laguna area on the east are a key area for understanding the complex depositional history of these strata. Two sequence boundaries at the K-2 and K-3 unconformities, four prominent marine-fl ooding surfaces at the top of the lower Oak Canyon Member and the tops of the Cubero, Paguate, and Twowells Sandstone Tongues of the Dakota, and two widespread bentonites in the upper Oak Canyon (A bentonite) and the lower Whitewater Arroyo Shale Tongue of the Mancos (X bentonite) are the key correlation surfaces on these outcrops. Progressively lower Morrison Formation strata, the Jackpile, Brushy Basin, and Westwater Canyon Members, are erosionally truncated westward along the basal Dakota unconformities. The basal Dakota Encinal Canyon Sandstone Member is only present in the Laguna area. The marginal marine and offshore Oak Canyon onlaps the K-2 unconformity, and the Dakota main body, an informal fl uvial unit derived from the west, onlaps the K-3 unconformity, which truncates the K-2 westward. The K-3 surface becomes a correlative conformity as the Dakota main body grades into shoreface Cubero Sandstone eastward. The Clay Mesa Shale Tongue of the Mancos wedges out westward between the Cubero and Paguate shoreface sandstones. The Whitewater Arroyo Shale and Twowells Sandstone at the top of the Dakota thin westward, but extend completely across the study area.