Geology of Monument Valley
Great sandstone layers once covered this region, but erosion has left the valley a wide flat plain, interrupted by formations that rise high into the air.
The area is a part of the Colorado Plateau, a region that covers 130,000 square miles within northwestern New Mexico, southeastern Utah, and northern Arizona. The elevation of the valley floor ranges from 5,000 to 6,000 feet above sea level. The floor is largely siltstone of the Cutler Group, or sand derived from it, deposited by the meandering rivers that carved the valley.
The iron oxide in the weathered siltstone gives the valley its red color. The blue-gray rocks in the valley contain manganese oxide.
The buttes are clearly stratified, with three principal layers. The lowest layer is Organ Rock shale (Permian), the middle de Chelly sandstone (Permian) and the top layer is Moenkopi shale (lower Triassic) capped by Shinarump siltstone (upper Triassic). Erosion of the soft shales of the Cutler Formation (Early Permian) revealed the buttes as vertically jointed slabs of sandstone.
The valley includes large stone structures including the famed “Eye of the Sun”.