The term “batholith” comes from the Greek bathos meaning depth and lithos meaning rock. Batholiths, simply put, are the result of molten material rising toward the earth’s surface. This material hardens into granite, a coarse-grained igneous rock. Some of this rock finds its way to the surface. Batholiths are not noted as distinct areas unless they cover at least 40 square miles. The Boulder Batholith extends roughly from Butte to Helena and covers around 100 square miles, a relatively small area compared with other batholiths. Listen to learn more…

This Field Note was written by Terry Habeger. Would you be interested in writing one? Contact Allison De Jong, Field Notes editor, at adejong [at] montananaturalist [dot] org or 406.327.0405. Please visit the Field Notes website at the Montana Natural History Center for more information.