| Spider Rock is a pinnacle in Canyon de Chelly. The De Chelly Sandstone (about 825 feet thick) consists of sand deposited in dunes and marginal sand sheet and sabka environments in a subtropical arid setting in Early Permian time. The thick and extensive deposit of dune sand is reminiscent of modern sand seas (called ergs), such as in the modern Sahara or Arabian Peninsula (Glennie, 1987). The caprock along the canyon consists of a comparatively thin unit of Shinarump Conglomerate. The Shinarump Conglomerate of the lower Chinle Formation is of Late Triassic age and consists of stream deposited sand and gravel. Moenkopi Formation which typically occurs below the Chinle Formation elsewhere on the Colorado Plateau is missing in the Canyon de Chelly region (Baars, 1995). Younger strata that once covered the region has long since eroded away. |
