Batholith

Batholith

 If you come across an outcrop (exposure) of coarse-grained igneous rock, chances are you are standing on a pluton or batholith that crystallized several km below the Earth's surface. It may represent the magma chamber of an extinct volcano or a magma body that never produced any eruptions.

Batholiths indicate a long period of repeated igneous intrusions over a large area, such as might be expected along a subduction zone.

The Sierra Nevada Batholith

The Sierra Nevada Batholith of eastern California forms the largest mountain range in the continental U.S. Although the prospect of walking across huge areas of one type of rock--granite--might seem dull, in fact the Sierras offer spectacular scenery and lots of interesting details about what went on in the magma chambers of a suite of subduction zone volcanoes that were active from roughly 150 to 80 million years ago. Intrusive rocks offer many clues as to the inner workings of the Earth!