The Washita Group in North-Central Texas and southeastern Oklahoma consists of up to 114 m of intercalated shale, limestone, and sandstone that accumulated in the shallow, epicontinental sea of the East Texas Basin. The Ouachita-Arbuckle Mountains to the north supplied terrigenous sediments, and the Central Texas platform to the south was a site of carbonate deposition leeward of the shelf margin of the Stuart City trend. Eleven lithofacies of the Washita were deposited within a repeatedly subsiding shelf basin that received an intermittent supply of terrigenous sediment. The deepest seaway formed after subsidence and was filled by a south-to-north progression of facies consisting of mollusk-echinoid wackestone on a shallow shelf, transitional packstone shale of deeper water, calcareous and sandy shales of the deepest water, thin-bedded sandstone of the shallower water shoreface, wavy lenticular sandstone and shale of the distal delta front, and deltaic estuarine trough-crossbedded sandstone. Following basin filling, the carbonate shelf prograded northward, grading into nearshore sediments. This produced the south-to-north succession of mollusk-echinoid wackestone to either oyster packstone shale, oyster packstone and quartzitic-oyster packstone or quartzitic mollusk-echinoid packstone of the shoreface.