The granite intrudes Archean and Lower-Middle Huronian rocks and is overlain unconformably by Upper Huronian sediments. The Duluth gabbro cut across and metamorphosed its southeastern edge. In general ...

A batholith is a large mass of intrusive igneous rock that made its way to the surface. While relatively small by world standards, the Boulder Batholith, and by extension the Boulder Mountains ...

But when you strike one of the rocks with a hammer, it emits an unexpected, resonant peal. The geological abnormality is part of the Boulder Batholith, a 1.2 million-acre mass of igneous rock ...