Plutonic Rocks are named for the Roman God of the Underworld, Pluto. The local mountains, the San Gabriel, San Bernardino, Santa Ana all have Mesozoic granitic rocks that formed when the offshore Farallon Plate was subducted under the North American Plate during the Mesozoic. The magma most certainly supplied volcanoes on the surface. Over time the magma reservoirs that fed the volcanoes on the surface cooled and formed batholiths primarily made of granite. These deep-seated batholiths at miles in depth are now exposed at the surface because over time erosion and uplift expose these features.
Dikes are intrusions that the liquid state squeeze up through existing country rock.
The feeder for a volcano is a dike. Know the Palisade Sill. Stocks are the intrusions that are large bulbous features that have fed off a magma chamber and are smaller than 40 square miles. They are distinguished by color. Remember the dark igneous rocks are high in iron silicate minerals and calcium feldspar while the light colored igneous rocks are high in silica rich minerals and potassium feldspar.