A batholith is a huge intrusion of magma that is usually many miles, sometimes hundreds of miles in diameter. The Sierra Nevada batholith forms the root of much of the Sierra Nevada Mountains in California. The Pikes Peak batholith, much of the root of the Colorado Front Range.
The magma chamber that formed the batholiths may or may not be connected to the surface by a vent where the magma may erupt as a volcano. Remaining magma within the vent solidifies to form a stock.