The Lower Cambrian Mural Formation of the Upper Proterozoic-Cambrian Cariboo Group extends northwest from Sandy Lake along Iltzul Ridge for 19 kilometres. The belt varies from 0.5 to 2.5 kilometres in width. Bedding generally strikes northwest and dips between 20 and 35 degrees northeast.

Two carbonate members separated by shale are contained within the formation. The lower member is comprised of oolitic and bioclastic fossiliferous limestone. The upper carbonate member is made up almost entirely of massive beds of dolomitic micrite.