The sandstone tongue of the Cherry Canyon Formation and the overlying upper San Andres Formation, exposed in the Last Chance Canyon area, represent a progradational sequence of slope, shelf, and nearshore systems. Based on lateral and vertical lithofacies relations, a paleoenvironmental model in a landward to basinward transect consists of the following: a supratidal through subtidal mixed carbonate-siliciclastic tidal flat; a mixed carbonate-siliciclastic lagoon; a fusulinid shelf shoal or bank complex; a predominantly carbonate open-marine

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shelf containing sporadic patch reefs; a predominantly siliciclastic slope.

Numerous basinward-trending channels, commonly about 35 m deep and 400 m wide, are incised into the shelf and slope systems. The channels were cut and filled by shelf-derived, saline density currents. Breaches created by storms in the shoal complex allowed dense saline water, which had accumulated in the lagoon, to spill basinward as gravity-driven underflows beneath the less dense normal-marine waters. The bottom-hugging currents dissected the shelf and slope systems eroding deep basinward-trending channels. Large volumes of lagoonal sediments were moved through the channels in traction transport, ultimately filling the channels. Eventually the flows that maintained the channels ceased, resulting in channel abandonment and annealing of the shelf shoals and a return to normal shelf an slope processes.

The sandstone-filled channels extend as subparallel non-bifurcating features far into the basin environment and thus differ markedly from radially branching submarine fan channels. In contrast to offlapping lobes observed in submarine fan deposits, the Delaware Mountain Group channels are probably backfilled, resulting in onlapping siliciclastic packages.

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