The country rocks near this prospect are pelitic schist and gneiss, and subordinate andesitic and basaltic metavolcanic rocks, that are intruded by Cretaceous stocks, sills, and dikes of feldspar-porphyritic granodiorite, and by small metadiorite plutons of undetermined age (Berg and others, 1988). The strata were regionally metamorphosed to upper greenschist or amphibolite grade in Cretaceous time, and, near some of the granodiorite contacts, subsequently contact metamorphosed to hornblende hornfels. The premetamorphic age range of the strata is unknown. Berg and others (1988, p. 17) assigned them an undivided Mesozoic or Paleozoic age. More recent studies suggest that at least some of the strata may be as old as Precambrian (Crawford and others, 2000).