Batholiths, such as those that make up the sierra nevada mountains of california, form at great depth in the crust. how could they have been exposed at the surface?

By uplift and erosion. Batholith, an expansive group of volcanic shake shaped underneath the Earth's surface by the interruption and cementing of magma. It is usually made out of coarse-grained rocks with a surface introduction of 100 square km or bigger.