Bisti and Horseshoe Canyon fields produce from stratigraphic traps formed by northwest-trending linear sandstone bodies enclosed in marine shale of Late Cretaceous age. Despite these similarities, the sandstone bodies originated by different depositional mechanisms. The lower Tocito reservoir at Horseshoe Canyon is an excellent example of post-unconformity sandstone, whereas the productive "Bisti" sandstone is a marine bar sandstone. At Horseshoe Canyon field, up to 90 ft (27 m) of sandy marine shale overlies the lower Tocito sandstone and separates it from the upper Tocito sandstone. The upper Tocito, which is also productive, is apparently a bar-type sandstone accumulation formed after deposition had essentially buried the erosion surface.

The marine bar-sandstone complex forming the Bisti field reservoir occurs at the approximate stratigraphic level of the productive units at Horseshoe Canyon field. Truncation at the erosion surface beneath the lower Tocito at Horseshoe Canyon field diminishes southward, toward the Bisti field. Petrographic studies have failed to establish the presence of the erosion surface at Bisti, despite the distinctive characteristics of this surface. The "Bisti" sandstone grades downward into sandy marine shale.

The reservoirs at these two fields illustrate the fact that superficial similarities in sandstone bodies do not necessarily mean an identical origin.