The Jurassic San Rafael Group, Four Corners region
— Spencer G. Lucas and Orin J. Anderson

The Jurassic San Rafael Group on the Colorado Plateau consists of six formations (in ascending order): Carmel, Entrada, Curtis, Todilto, Summerville and Bluff. Unconformities (J-2 below and J-5 above) bound the San Rafael group, and a within-group unconformity (J-3) separates the Curtis and Todilto Formations from the underlying Entrada. The Page Sandstone is here considered the Page Member of the Navajo Sandstone and not included in the San Rafael Group. The J-2 unconformity is at the Page- Carmel contact, not at the Page-Navajo contact as claimed by some workers. The Dewey Bridge Member of the Entrada Sandstone in Utah-Colorado is correlative to part of the Carmel Formation, and it may correlate to the medial silty member of the Entrada Sandstone in the San Juan Basin, New Mexico. If so, the Iyanbito Member of the Entrada Sandstone in the southern San Juan Basin is older than the J-2 unconformity and a correlative of part of the Glen Canyon Group, probably the Navajo Sandstone. The Entrada Sandstone represents an erg that covered much of the Southwest during late Carmel and post- Cannel time. Early transgression of the Curtis-Sundance seaway across the Entrada erg produced a salina basin in northern New Mexico/southwestern Colorado in which the Todilto Formation was deposited. Continued transgression created a vast paralic facies tract that extended from east–central Utah into southeastern Colorado, northeastern New Mexico and northwestern Oklahoma in which the Summerville Formation was deposited. The Summerville Formation consists of the (lower) Beclabito Member, present throughout the Summerville outcrop belt, and the (upper) Tidwell Member, only present in Utah and southwestern Colorado. The Tidwell Member occupies the same stratigraphic position as and is correlative with the Bluff Sandstone. The Bluff Sandstone (Junction Creek Sandstone is a synonym) consists of the main body (lower) and Recapture Member. The Recapture Member is cyclically bedded sandstones and siltstones strikingly similar to strata of the Summerville Formation. Cow Springs Sandstone is a synonym of Zuni Sandstone. The J-5 unconformity marks the boundary between the youngest San Rafael Group strata and the basal, Salt Wash Member of the Morrison Formation. Fossils, regional stratigraphic relationships and radioisotopic ages support the following age assignments to units of the San Rafael Group: Carmel = middle to late Bajocian; Entrada = Bathonian to early Callovian; Curtis = Todilto = middle Callovian; Summerville = middle Callovian to Oxfordian; and Bluff = Oxfordian.