The region is underlain by the Coast Plutonic Complex, consist- ing of pre- to post-kinematic quartz diorite to granodiorite batho- liths intruded into Paleozoic to Mesozoic metasedimentary and meta- volcanic rocks. Younger supracrustal assemblages overlying deformed rocks include the (?)Cretaceous Gambier Group and Tertiary Bella Bella Formation volcanic rocks.

The underlying geology of the Nascall hot springs area consists of foliated quartz diorite. The temperature of the water in the hot spring has been estimated at 40 to 50 degrees celsius, however, no information on its composition is available.