The southern section has undifferentiated alluvial and colluvial deposits overlying Jurassic and early Cretaceous graywacke and chert formations. The active layer of the permafrost is generally less than 1 m, except beneath large rivers, where thawing may be deeper. Drainage in the Arctic Foothills Ecoregion is integrated. Major streams originate from the Brooks Range and are structurally controlled by the bedrock. Most streams are swift, but portions may be braided across gravel flats.
Perennial streams have algae-covered rocky bottoms.
During spring snowmelt and breakup of river ice, flooding and channel shifting are common. Oxbow lakes along major stream valleys are the predominant type of lake in this ecoregion. Most lake beds are organic muck, but some are sandy. Soils Principal soils are Histic Pergelic Cryaquepts, Pergelic Cryaquepts, and Pergelic Ruptic-Histic Cryaquepts. Dominant soils in valleys and on long slopes formed in silty or loamy colluvial sediments.