A belt of limestone of the Hadrynian Cunningham Formation (Cariboo Group) outcrops in the vicinity of Cunningham Pass and Cunningham North Mountain and continues northwest for 21 kilometres to 8 Mile Lake. The belt follows the crest of the Cunningham anticline, which is segmented by a series of northeast trending faults. Overlying chloritic schists, phyllites and quartzites of the Yankee Belle Formation (Cariboo Group) flank the belt to the east and west. The belt varies up to 2.2 kilometres wide.

The Cunningham Pass deposit is comprised of massive, fine grained, grey limestone that is hydrothermally altered over widespread areas to light grey and buff mottled, medium grained ferroan dolomite. The limestone is commonly cut by thin white calcite veinlets. Some argillaceous layers become more numerous near the top of the formation. In thin section the rock displays up to 5 percent in detrital quartz and calcite.