One can't think of Canyon De Chelly (pronounced "Duh Shay") without thinking of the Spider Rock and the towering, Permian De Chelly Sandstone cliffs. In much of this area, the De Chelly Ss is protected by a thin cap of Shinarump Conglomerate (Chinle Fm) without which the vertical walls couldn't exist. The De Chelly Ss "pinches out" near Monument Valley and Mexican Hat, UT where it overlies the Organ Rock Shale and the top is eroded off prior to deposition of Triassic aged rocks (the Chinle Fm).

Condon, Steven M., 1997, Geology of the Pennsylvanian and Permian Cutler Group and Permian Kaibab Limestone in the Paradox Basin, Southeastern Utah and Southwestern Colorado, US Geological Survey Bulletin 2000-P, pp. 56.