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This limestone sink in the foreground was formed when the roof of a cavern in the Kaibab Limestone collapsed, probably plugging the outlet and allowing a pond to form. There is another sink 2 miles (3.2 km) to the south, and ruins are clustered around its edge also. The thick Kaibab Limestone forms the greatest portion of the walls of the sinkhole. It is stained by seepage from the overlying red Moenkopi Sandstone, a thin layer of which can be seen at the base of the black lava which forms the surface.