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Restoration of an Urban National Park Service Setting Three Case Studies William Godwin, PG, CEG
Figure 1. Vicinity and geologic map by Blake et al (2000). GGB – Golden Gate Bridge. No scale.
Introduction This paper presents the geologic aspects of recent restoration efforts on National Park Service (NPS) facilities that allow reuse by members of the public in addition to geoscientists. The three case studies presented examine the background and geologic basis for remediation and restoration of infrastructure that provides both historic and current access to these areas. The three cases studies, whose locations are shown in Figure 1, consist of the Point Bonita Lighthouse Bridge replacement, the Baker Beach Disposal Area (BBDA) removal, and the Presidio Parkway replacement of Doyle Drive.
History and Geologic Setting The Golden Gate National Recreation Area (GGNRA) is one of the largest urban national parks in the world. Established in 1972 to bring “parks to the people,” GGNRA’s nearly 76,000 acres of land and water extend north of the Golden Gate Bridge to Tomales Bay in Marin County and south to San Mateo County in coastal California. Most of the GGNRA occupies the coastline and was originally developed to support military fortifications and shipping navigation.
Spring 2022
The subject area is located in California’s Coast Ranges geomorphic province, an approximately 500-mile-long series of northwest-trending mountain ranges (2,000 to 6,000 feet elevation) and valleys that generally trend subparallel to the San Andreas Fault. The geomorphology of the Coast Ranges province is controlled predominantly by deformation (faulting, folding, and shearing) associated with subduction of the Farallon Plate beneath the North American Plate and movement between the Pacific and North American Plates along the San Andreas Fault system. The geology of the Coast Ranges province features several terranes, which are distinct blocks or assemblages of Cretaceous and Jurassic, igneous and sedimentary oceanic rock scraped off the Farallon Plate during its subduction and metamorphosed (or not) to varying degrees. These terranes and associated mélange zones are collectively called the Franciscan Complex. In the Bay area, the Franciscan Complex is divided into the eastern and the central belts, with the older eastern belt lying structurally higher and being of higher metamorphic grade than the central belt. In Figure 2, William Elder (geologist with the National Park Service) shows that San Francisco and the Marin Headlands contain three of these terranes, from oldest to
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