Geologic mapping in the Killik River and Chandler Lake quadrangles has delineated rocks of at least three of the major allochthons found in the De Long Mountains of the western Brooks Range: the Brooks Range (Endicott Mountains), Picnic Creek, and Copter Peak allochthons. Rocks characteristic of parts of the Tpnavik River and Nuka Ridge allochthons are also present.

The Endicott Mountains allochthon forms the main crest and mountain front of the central Brooks Range. It is the structurally lowest of the allochthons in the region. Major rock units on the allochthon are: Upper Devonian Hunt Fork Shale and Noatak Sandstone, Upper Devonian-Lower Mississippian Kanayut Conglomerate, and Mississippian Kayak Shale of the Endicott Group; Alapah Limestone and Kuna formation of the Lisburne Group; and Permian Siksikpuk Formation and Triassic Otuk formation of the Etivluk group. Lower Cretaceous coquinoid limestone and, in some places, orogenic sediments of the Okpikruak Formation cap the allochthon. Total stratigraphic thickness of the Endicott Mountains allochthon is over 2,000 m (6,500 ft).

Rocks of the Picnic Creek allochthon are widespread in the "disturbed belt" of the Brooks Range foothills, and structurally overlie the Endicott Mountains (Brooks Range) allochthon in the Killik River quadrangle and quadrangles to the west. The allochthon is not recognized with certainty east of the Killik River quadrangle. Major rock units on the Picnic Creek allochthon are: Upper Devonian(?) Hunt Fork Shale, Lower Mississippian Kurupa sandstone tongue (new name) of the Noatak Sandstone, and Mississippian Kayak Shale of the Endicott Group; Carboniferous Akmalik chert (new name) of the Lisburne Group; and Pennsylvanian Imnaitchiak chert (new name) and Otuk formation of the Etivluk group. Orogenic sediments of the Lower Cretaceous Okpikruak Formation form the top of the Picnic Creek al ochthon. Total stratigraphic thickness of these rock units is not over 1,000 m (3,200 ft).

Plant fossils from a number of localities in the Kurupa sandstone are dated as Early Mississippian (Tournaisian-Visean) by B. A. Thomas and R. A. Spicer and have close affinities to material from eastern USSR. Palinspastic restoration of the Picnic Creek allochthon southward to a position south of the Endicott Mountains allochthon restores the Kurupa sandstone, the Akmalik chert, and the Imnaitchiak chert to their proper basin position. In the reconstructed basin, the Kurupa sandstone appears to represent the distal, southern end of the Kanayut-Noatak coarse-clastic wedge. The Akmalik chert and Imnaitchiak chert represent basinal equivalents of the Alapah Limestone-Kuna formation of the Lisburne Group and Siksikpuk Formation of the Etivluk group.

Detailed stratigraphic and paleontologic studies of the Mississippian through Triassic rocks on both allochthons are in progress.

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