The Muller area is underlain by rocks of the pre-Jurassic Westcoast Complex. This complex is a heterogeneous assemblage of hornblende-plagioclase gneiss, amphibolite, agmatite, basic migmatite, quartz diorite or tonalite and minor metasedimentary and metavolcanic rocks. It is genetically related to the Jurassic Island Intrusions, and considered to be derived from Sicker and Vancouver Group rocks. Small areas of limestone belonging to the Upper Upper Paleozoic Buttle Lake Group, also occur in the area.

Muller reports the occurrence of an iron skarn outcropping on a ridge between Tofino and Tranquil creeks, 1 kilometre north of the 4046 foot (1233 metres) elevation mark. The deposit consists of a vertical lens of magnetite that is up to 6 metres wide but pinches out within 30 metres (Geological Survey of Canada, Paper 66-1).