West Spanish Peak monzonite. West Spanish Peak syenite porphyry radial dikes. White Peaks microgranite. Late phase subparallel dikes north and northwest of East Spanish Peak. Igneous rocks of the region display considerable range in compositions, which may be described in general as either felsic or mafic.
Some rocks have compositions intermediate between felsic and mafic.
The most common felsic rock compositions are monzonite and syenite porphyries. These rock types form the stocks of major intrusions and most of the dikes near to Spanish Peaks. Mafic rocks, such as basalt , are found farther away from Spanish Peaks. See Spanish Peaks igneous petrology by Brian Penn. See igneous rock classification.