The Permian of southern Utah, northern Arizona, northwestern New Mexico, and southwestern Colorado is conceived as bounded below, except in the Grand Canyon, by conformable Pennsylvanian limestone (Callville limestone in the extreme west, an unnamed unit in north-central Arizona, Hermosa formation in San Juan Valley and southwestern Colorado, Magdalena limestone in northwestern New Mexico), and above by unconformable Triassic deposits (Moenkopi formation, Shinarump conglomerate, and Dolores formation, in order from west to east). In the Grand Canyon the underlying beds are Mississippian (Redwall) limestone. Three main types of Permian sequence occur: that of the Grand Canyon, with the Supai formation and Hermit shale (red beds), Coconino sandstone (light-colored, cross-bedded), and Kaibab limestone, named in ascending order; that of Monument Valley and adjacent country north and south, with the Rico formation (red beds and limestone) below and five units above, here treated as parts of the Cutler formation and named in ascending order the Halgaito tongue (red beds), Cedar Mesa sandstone member (light-colored, cross-bedded), Organ Rock tongue (red beds), De Chelly sandstone member (light-colored, cross-bedded), and Hoskinini tongue (red beds); that of southwestern Colorado, with the Rico formation (red beds and limestone) below and the undivided Cutler formation (red beds) above. The relations of these units to one another are shown in a number of cross sections and the earlier nomenclatures are correlated with that used here. Apparently the Permian began with the widespread deposition of red beds derived from the east, except in the extreme west part of the area where light-colored sands were laid down. In the east a few marine limestones (Rico) interrupted the sequence of red materials, representing incursions of a sea from the east. These first red deposits were followed by light-colored sands coming from the northwest (Cononino, et cetera), which interfingered with the red materials that still continued to come in from the east. Then marine waters gradually advanced from the west across the western half of the area, depositing chiefly limestone (Kaibab). East of the sea the light-colored sandstones were the chief deposits in a wide zone, and still farther east the red materials prevailed. Finally, the sea withdrew with seeming abruptness and the whole area was exposed to the period of erosion represented by the unconformity at the base of the Triassic.