Northernmost Ellesmere Island contains a geological province known as Pearya, now regarded as an exotic continental fragment with an internal suture (Trettin, 1991). Pearya appears to have been part of the Caledonides mobile belt until at least Late Ordovician time, and was probably accreted to the Franklinian mobile belt after the Late Silurian (Trettin, 1991). The geologic history of Pearya includes five orogenies; one of these, the Middle Ordovician M'Clintock Orogeny, is comparable in age and character to the Taconic Orogeny of eastern North America (Trettin, 1987b). Pearya has been divided into four major successions, ranging from late middle Proterozoic (Neohelikian) to Late Silurian in age, and differing in lithology (Trettin, 1991). Two of these lithologic successions are represented in the Lake C2 watershed (III and IV), separated by an angular unconformity (Geological map).
The lithologic descriptions below of successions III and IV follow those of Trettin (1987a, [1990?] and 1991). Succession III underlies the western portion of the watershed, which is largely below 1500 ft (460 m) a.s.l. (Geological map). The volcanics of the Maskell Inlet Assemblage are primarily made up of tuffs, with lesser flows. Compositionally these are mostly andesite or undifferentiated andesite/basalt. These greenish gray or dusty red rocks (Trettin, 1987a) were abundant in the stream channel bed during the present study. Sediments in the Assemblage are mostly limestone, chert, and mudrock, along with lesser proportions of sandstone and dolostone (Trettin, 1991). Most rocks in succession III indicate subgreenschist or greenschist facies metamorphism.
Two formations of succession IV are exposed in the watershed. In the northeastern part, the Ayles Formation is comprised of dolostone, calcareous dolostone and dolomitic limestone. Fossils are rare. Strata of the Ayles Formation are very resistant (Trettin, 1987a), and in fact the highest elevation of the basin is within the Ayles Formation (unofficially named White Mountain). The remainder of the watershed is underlain by Member A of the Cape Discovery Formation. Moving upward, Member A is made up of upward-fining conglomerate, sandstone, and calcareous and dolomitic sandstone with a variety of benthonic fossils (observed all along the inlet stream channel), and tuffs and flows of felsic to mafic composition. Thrust faults within the watershed, between the Maskell Inlet Assemblage and the Cape Discovery Formation, are associated with the Taconite River Fault Zone. These faults closely coincide with the two stream valleys draining the upper watershed, and are nicely highlighted by the prominence of a large mountain, unofficially named Black Peak (Geological map).
Within the Lake C2 watershed, some lithologies are probably more important sources of fluvial sediments than others. Delineating these source areas on the geological map is difficult, however, because the Cape Discovery Formation and Maskell Inlet Assemblage are both so lithologically diverse. However, the high elevation northeastern portion of the watershed may be relatively less important than other areas, due to the relative resistance of dolostone.