ADULT EDUCATION IN GOLDEN GATE NATIONAL RECREATION AREA, SAN FRANCISCO BAY REGION, CALIFORNIA
GGNRA includes rocks that formed at divergent, convergent, and transform plate boundaries and that record interactions of the North American, Pacific, and Farallon plates during the past 200 Ma. The Marin Headlands north of the Golden Gate Bridge include Mesozoic pillow basalts that formed on the Farallon plate at a divergent boundary, and the overlying radiolarian ribbon cherts record 100 Ma of starved sedimentation as the plate traveled across the Pacific Basin. The serpentine, sandstone/shale mélange, and metamorphic blocks of the Franciscan complex near the south side of the Golden Gate Bridge record subduction processes and development of shear zones at a convergent plate boundary. The Franciscan subduction complex of the North American plate is separated from the granitic basement rocks of the Salinian terrane on the Pacific plate at Point Reyes National Seashore by the San Andreas transform fault. The Salinian terrane records significant lateral displacement from at least Southern California.
The class discussions also focus on Quaternary climatic cycles and resulting sea level fluctuations as well as their influence on the evolution of San Francisco Bay and surrounding areas. Finally, the topic of man as an agent of geologic change in the Bay Area is related to historical events since the gold rush of 1849. Teaching adult education courses in GGNRA is extremely rewarding because of the students genuine interest in geology and their desire to learn about the processes that shaped familiar landscapes through time and space.