Geology
The mesa is topped by a hard volcanic basalt. This layer, formed approximately 10 million years ago by basalt flows, suppressed erosion compared to the surrounding sedimentary rock layers, which suffered rapid downcutting from the action of the Colorado and the Gunnison rivers. The top layer rests on a thick sequence of Eocene shale and sandstone known as the Green River and Wasatch Formations. These layers in turn rest on a Cretaceous layer known as the Mesaverde Group that forms a cliff about halfway up the side of the mesa. The lowest layers are yellow and gray Mancos Shale of late Cretaceous age. The shale continues outward into the surrounding valleys in the vicinity of the mesa, providing a soil base that is fertile for various kinds of agriculture, especially in the Gunnison Valley to the south.
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