The Kaiparowits Plateau comprises a 2-km-thick sequence of Upper Cretaceous rocks. The oldest Cretaceous unit in the sequence, the Dakota Formation, has Cenomanian palynomorphs in the middle nonmarine member and late Cenomanian molluscs in the overlying marine member. The Tropic Shale has been dated by marine molluscs as latest Cenomanian to middle Turonian. The Straight Cliffs Formation spans the middle Turonian through the Santonian and has been divided into four members. The Tibbet Canyon Member is of middle Turonian age, based on inoceramid bivalves, and the overlying terrestrial Smoky Hollow Member, though undated, is probably late Turonian in age. An unconformity of latest Turonian age separates the top of the Smoky Hollow Member from the overlying member. Molluscs in the marine facies of the John Henry Member indicate an early Coniacian through Santonian age. The overlying Drip Tank Member is undated. The Straight Cliffs Formation thickens northward across the Kaiparowits basin, indicating greater rates of subsidence in that direction. The overlying Wahweap Formation is considered to be of early Campanian age on the basis of its mammalian fauna. It is divided here into four informal members. The Kaiparowits Formation is middle to late Campanian in age, based on mammalian faunas and reevaluation of previously reported palynofloras. The Canaan Peak Formation has been dated as late Campanian based on palynomorphs, and if this date is valid, the folding and erosion of the underlying sequence occurred very rapidly near the end of the Campanian.