In the Tatsamenie Lake area, intensely folded and regionally metamorphosed Permian, Triassic and older strata of the Stikinia Terrane, are separated from less folded and less metamorphosed Mesozoic sedimentary and volcanic rocks by a pre-Upper Triassic unconformity. Foliated hornblende diorite of Juro-Triassic Age intrude the pre-Upper Triassic rocks.

The Permian strata consists of a 760 metre succession of limestone and dolomitic limestone, with local chert, shale and sandstone. The succession is best exposed in the cores of north trending anticlines south and east of Tatsamenie Lake. The limestone is massive to well bedded, usually fine-grained and medium grey in colour. It contains fusulinids, crinoids and shell and coral debris. Many areas of the limestone have been thermally recrystallized and silicified.