Most of the Mule Hole watershed is developed on paragneiss (peninsular gneiss) and basic rocks (amphibolite and derived facies). The latter cover about 17% of the watershed and are not related to any particular topographic locations. They can be found anywhere namely in the valley bottom, along the slope or on the crest line. Paragneiss is dominant and consist mainly of quartz, feldspar (plagioclase and potassic) with a low quantity of biotite. Bedrock exposures are usually poorly weathered, except along the talweg at the higher third of the watershed where the gneiss occurs as non-cohesive loose saprolite (Figure 3).