The foothills foldbelt of the NPRA takes its name from its well-developed concentric folds involving Cretaceous rocks. These folds can extend over several townships, some being 40 mi (65 km) long and 10 mi (15 km) wide, and could contain significant amounts of oil. One fundamental problem in the foldbelt is to identify good quality reservoir rocks at optimum depths of burial.

The most widespread units containing potential reservoir rocks are the Torok Formation and the Nanushuk Group. The Torok Formation, of Aptian-Albian age, consists primarily of shale and siltstone with sands interbedded locally. It was deposited as a prograding delta sequence containing both marine and transitional marine clastics. The Nanushuk Group, of Albian to Cenomanian age, is typified by marine clastics grading upward into fluvial and nonmarine clastics. The Nanushuk Group contains many intervals with good reservoir potential, but they usually lie too near the surface to allow economical recovery of oil. The Torok lies at optimum depths, but it tends to be too fine grained or "dirty" to possess good porosities and permeabilities.

The Torok does contain certain intervals with better quality and more numerous sands. These sands were probably deposited as nearshore bars during periods of higher energy deposition. Seismic subsequences within the Torok are thought to represent large deltaic lobes. The tops of the subsequences are defined by zones of toplap or truncation and tie very well with the bases of sandier intervals near the transition from Torok to Nanushuk Group where the intervals are present in outcrop.

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