The upper Jurassic Morrison Formation in the Four Corners region
— Orin J. Anderson and Spencer G. Lucas

Nonmarine strata of the Morrison Formation are widespread in the Four Corners region. The Morrison Formation (Upper Jurassic)-San Rafael Group (Middle–Upper(?) Jurassic) contact is placed at a regionally traceable unconformity and sequence boundary at the base of the Salt Wash Member of the Morrison Formation. The internal stratigraphy of the Morrison is thereby simplified with only two members, the Salt Wash and the Brushy Basin, recognized for regional correlation purposes. Thus, the confusing, duplicative, and overlapping Morrison members which included Bluff, Recapture Shale, and Westwater Canyon Sandstone are no longer recognized, and the names are either abandoned or the units reassigned to the San Rafael Group. This Morrison concept and internal stratigraphy recognizes and follows useful mapping units that aid in regional correlation. The sequence boundary at the base of the Morrison records the onset of fluvial deposition and a climatic change related to northward drift of the North American continent through Jurassic time. Morrison deposition took place on riverine floodplains. A lacustrine origin for the Brushy Basin Member (ancient Lake T'oo'dichi') is not supported by several lines of evidence. Most age data suggest the Morrison Formation is of Late Jurassic age, but it still remains possible that the upper part of the formation is of Early Cretaceous age.