The Cutler red beds are a layer of red siltstone and shales characterized by red, reddish-brown and purple colors that were deposited during Permian time and that are very extensive on the Colorado Plateau. These rock layers were deposited by meandering streams moving through low, gently sloping country and carrying sediments from the Ancestral Rockies in Utah and Colorado. These sediments were exposed to highly oxidizing conditions throughout the erosion and sedimentation process, accounting for the high level of iron oxides in the rocks and thus their color. Only the very fine grain sands made it as far south as Monument Valley and Canyon de Chelly. Even so, as much as 600 feet of this red Cutler Formation are exposed in a canyon near Fort Defiance, AZ (near Window Rock).
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