The rocks immediately surrounding Forest Falls are basement rocks characteristic of the major part of the San Bernardino Mountains, that is, Paleoproterozoic gneiss, Neoproterozoic to Paleozoic marble and quartzite, and Late Cretaceous granitic rocks.
In central Manitoba lies the Flin Flon greenstone belt, which is one of the largest Paleoproterozoic volcanic-hosted massive sulphide districts in the world, containing 27 copper-zinc-(gold) deposits from which more than 183 million tonnes of sulphide have been mined.