The Defiance Uplift is an elongated uplifted region extending from the Four Corners region to Interstate 40, just inside the Arizona border. The uplift is a north-south anticline extending over 100 miles. This entire structure was relatively high throughout Paleozoic time. This rather gently uplifted island thus provided few sediments to the surrounding basins and seaways. It did however act as an effective deterrent to marine circulation between the adjacent basin regions, the San Juan Basin to the east and the Black Mesa Basin to the west.
The de Chelly sandstone can be traced to the crest of the Defiance uplift where it has thinned to only 200 feet near Fort Defiance. The entire set of Permian sandstones plunges beneath the surface of the Mesozoic strata where the axis of the uplift reaches Interstate 40 as it crosses into New Mexico.
Navajo route 12 runs north-south, on the west side beneath the crest of the plateau, connecting the reservations towns of Mexican Water, Rock Point, Round Rock, Lukachukai, Tsaile, Wheatfields, Crystal, Navajo, Fort Defiance, and Window Rock.
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