The area is underlain by the Eocene-Oligocene Carmanah Group, Hesquiat Formation which is comprised of siltstone, shale, sandstone and conglomerate.

Jeletsky (Geological Survey of Canada, Paper 53-17, page 63) reports the occurrence of "numerous fragments and pebbles of coal in a zone of breccia-like rock". He interprets the fragments as possibly having been mobilized from coal seams elsewhere.