Fig. 6. Photomicrograph of amphibolite dike rock (andesite porphyry), extending north-south through the Bonsall tonalite and Woodson Mountain granite (Fig. 3). The dike has nearly the same composition as the Bonsall tonalite (quartz diorite) but is finer grained. Biotite and hornblende (brown); zoned plagioclase phenocrysts (gray, cream, and white).