In the area of Last Chance Canyon the sandstone tongue of the Permian Cherry Canyon Formation, the subjacent lower San Andres, and the superjacent upper San Andres formations accumulated in a submarine canyon that extended from the Delaware basin margin northwestward into the Northwestern shelf. The Cherry Canyon tongue thickens basinward from the outcrop area which is 3-5 miles northwest of the Cherry Canyon basin margin. Early during the time of San Andres deposition, axial water depth in the canyon may have been as much as 600-1,000 feet. The presence of intertidal deposits in the lower Grayburg, including northwest-southeast flood and ebb-current directions, indicates that the canyon had shoaled sufficiently to become a tidal inlet.

Submarine-canyon deposits consist predominantly of narrow, deeply incised channels which are filled with massive, laminated, and current-rippled flow units, and numerous beds of conglomeratic carbonate-mudstone. The conglomeratic carbonate-mudstone beds commonly have hummocky upper surfaces and represent mud flow, slump, and avalanche deposits. In the lower San Andres and Cherry Canyon tongue, channel axes are inclined 4°-10°.

Orientation of channels, large and small current ripples, and aligned fusulines record a highly uniform southeasterly current flow pattern (i.e., down the canyon axis).

The fauna of the canyon deposits is primarily a thanatocoenosis consisting of shallow-water marine invertebrates (fusulines, corals, bryozoans, brachiopods, mollusks, trilobites, crinoid columnals, and echinoid spines). Burrowing organisms have homogenized thick intervals. The sediments contain large amounts of plant material and other organic matter.

The canyon headed in a shelf lagoon on the broad Northwestern shelf of the Delaware basin. When the lagoon was constricted, clastics were prograded across it and intercepted by canyon heads. When the canyon was expanded little or no clastic sediment reached the canyon and carbonates accumulated on the shelf and in the canyon.

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