The eastern part of the northern Interior Plains is underlain by rocks of Cenozoic, Mesozoic, and Paleozoic age. The region is bounded on the east by the Coppermine arch, composed of lower Paleozoic and Precambrian rocks. The plains region is a northwest-dipping homocline, interrupted in its western part by the Kugaluk arch, a north-trending pre-Cretaceous uplift.

Mesozoic rocks of the Interior Plains consist of Cretaceous sandstones, mudstones, and shales with a composite thickness of about 3,000 ft (900 m) along Anderson and Horton Rivers. The Lower Cretaceous units are correlated with similar rocks on Banks Island. On the mainland, these strata are disconformably overlain by varicolored clastic units of Late Cretaceous and early Tertiary age.

Westward, in the region of the Mackenzie delta, the Tertiary Reindeer Formation consists of a northward-thickening sequence of poorly consolidated to unconsolidated cherty gravels, crossbedded sands, and coal and ash beds. Its maximum outcrop thickness is about 4,000 ft (1,250 m). In the nearby B.A.-Shell-I.O.E. Reindeer D-27 well, the Reindeer Formation is 3,970 ft (1,210 m) thick and underlies 790 ft (250 m) of Quaternary and recent sediments. Microfaunal studies show that the Reindeer Formation overlies 2,200 ft (670 m) of Late Cretaceous clastic rocks which, in part, may be equivalent to the Moose Channel Formation, which crops out on the west side of the delta adjacent to the Richardson Mountains. These Upper Cretaceous rocks in the Reindeer well lie unconformably on 5,690 ft (1, 50 m) of Lower Cretaceous sandstones and mudstones which can be correlated with similar units in the eastern Richardson Mountains.

Offshore seismic profiles obtained during the 1969 Arcticquest survey indicate the presence of a thick sequence of sedimentary rocks, the lower part of which has been deformed into broad domal structures. These lower rocks are unconformably overlain by nearly flat-lying younger rocks. This unconformity may be the same as that separating the Lower and Upper Cretaceous rocks in the Reindeer well. Analyses of the profiles indicate that these younger rocks may have been intruded by diapiric structures.