Protogaea Civica I (Franciscan Formation/San Francisco, CA)

Geologic flag installation: San Francisco CA, 2004

Left: view of flags from Russian Hill, San Francisco towards the north, Alcatraz and Angel Islands in the background

Left center: detail view of flags, looking south: Flag sequence from top:Reinforced Concrete; Ferruginous Radiolarian Chert;
Meta-basalt/Greenstone; Graywacke/Metagraywacke Sandstone; Shale Matrix Melange/Shear Zone; Serpentinite.

Right center: Geology Flags Project: Protogaea Civica I (Franciscan Formation, San Francisco, CA),
cross section, and map showing basement geology and location of flag - center of orange circle.

Far right: Geology Flags: Master Legend - Basic Rock Types/Structures, A legend of symbols and graphic representations for a general range of sedimentary, metamorphic,
igneous and anthroturbational geologic materials used to generate flag images representing site-specific geologic information for the Geology Flags Project.

Protogaea Civica I (Franciscan Formation/San Francisco, CA)

Six flags, from The Geology Flags Project, depicting the geologic materials and some structural relationships of Holocene architecture and the major rock units of the Mesozoic and Cenozoic Franciscan Formation, San Francisco, CA; the top flag represents, reinforced concrete, a Holocene Era formation.

These flags, designed for the geology of San Francisco, focus on the primary rock units of the Franciscan Formation, including: meta-graywacke, radiolarian chert, serpentine, melange and meta-basites as well as a Holocene architectural material of the built environment, reinforced concrete. Commission and installation of the Protogaea Civica I (Franciscan Formation/San Francisco, CA) was done for the 'Topographies Exhibition' at the San Francisco Art Institute, March 18 - May 8, 2004. curated by Karen Moss. Protogaea Civica II (Franciscan Formation/San Francisco, CA), 2005 and Protogaea Civica III (Santa Rosa), 2006, are more recent works in this series.

The complete set of flags of the Geology Flags Project are envisioned as a comprehensive system of geo-taxonomy, an indexing and revealing of the geologic materials and structures beneath any given site. The full expression of the flag system would have a range from pure chemical elements through mineralogy, paleontology, processes, materials, formations, tectonic structures and architectural analogs present above, beneath and/or extending from a site of study.

The diagrams on the flags are derived from geologic and architectural symbols for materials and processes and can be used in different combinations to describe any site with new flags for special or new attributes being generated as needed. The ideal installation would involve numerous flagpoles distributed throughout an extended site with appropriate flags on each pole indicating the lateral changes in geologic information below, like free-standing core samples. The architectural extension of the geologic materials displayed as flags at appropriate sites correlates the built environment and the contemporary Holocene era with subterranean materials and time frames. This idea refers to the concept of anthroturbation, described in an essay written about the work, Holocene Terrace, shown at Lance Fung Gallery, NY, NY, 1999, an extract follows:

" Cities, architecture, roads and other civic constructions made by mankind of earth materials during our Epoch (the Holocene) may be considered in a geologic context as forms of "anthroturbation."1 This term describes the disturbance, dislocation and restructuring of geologic formations and materials by human agencies into new forms. These processes have analogies in the natural world, such as: mining as erosion, transport as flow and construction as sedimentation. Likewise, the built topography of a city can be understood in geomorphic terms: streets as canyons, buildings as plateaus, sewers as caves and plazas as playas."

1 A term developed in conversation with the geophysicist, Paul Spudich.

NOTES: Study: Geology Flags Project/Franciscan Formation/San Francisco, CA

The intention of the map and section is not geologic accuracy or authority but to give an idea of the complexity and richness of the Franciscan Formation (also known as the Franciscan Complex) and to relate the Geologic Flags to Bay Area geology in a large area proximate to 555 Beach St, San Francisco, the location of the flag pole where the flags have been installed (see map and images above) for the Spring of 2004. The patterns used on the Flags and corresponding designs indicating the rocks and structures on the map were derived from a larger geologic indexing and identification system for nearly all rock types, see the drawing: Study: Geology Flags - Basic Rock Types/Structures, above. The anthroturbation elements (human built architecture and structures) represented by the top most flag (reinforced concrete) and recent (Quaternary) surficial deposits (primarily soils, sands and alluvium) are not shown on the map for reasons of clarity as most of the urban areas of map are covered by these materials.

Geologists understanding of the Bay Area geology and the Franciscan Complex has evolved considerably since the acceptance of the theory of plate tectonics since the 1960Õs and its role in the accretion and emplacement of marine sediments, volcanics and crust that comprise the outer coast ranges of California.

It is now seen that the Franciscan Complex of the California Coast Ranges was formed as a subduction complex related to east-dipping subduction along the western North American plate margin from the Late Jurassic through the Early Tertiary, this occurred over a period of at least 140 million years (Wakabayashi, 1992a). The Franciscan is part of an 800 km long assemblage of similar rocks along the west coast of North America. The main rocks of the Franciscan Complex are predominately marine sedimentary rocks such as sandstone and shale with lesser amounts of marine basaltic rocks and chert as well as serpentinite, a hydro thermally altered ultramafic (low silica, high iron and magnesium) oceanic crust. Melange zones that contain exotic blocks of other Franciscan rocks in a sheared shale or clay matrix often separate more coherent thrust sheets. In regions that are not significantly altered by Cenozoic deformation, Franciscan rock units, including melanges, comprise a stack of nappes (terranes, e. g., Alcatraz Terrane) similar to structures that are used to describe the European Alps (Seiders, 1991; Wakabayashi, 1992, 1999). Apparent accretion ages of the nappes show them to be younger structurally downward, which is a reverse of the normal depositional order of younger rock on top of older rocks. This structure suggests emplacement as a result of progressive underplating or offscraping in the subduction zone trench during the process of subduction (Seiders, 1991; Wakabayashi, 1992). Some of the sedimentary (graywacke sandstone, radiolarian cherts) and volcanics (basalts) have been metamorphosed by the heat and pressure of subduction process, some at depths of 25 to 30 km, or more before being revealed at the surface by uplift and erosion (Wakabayashi, 1999); meta-graywacke, meta-cherts and meta-basites (greenstones) are the corresponding metamorphic names. The active subduction process, which still continues north of the Mendocino Triple Junction off the Mendocino coast to the north, ended in the Bay Area about 25 million years ago with the formation of the San Andreas fault (Konigsmark, 1998).

General and Cited Professional References:

Alt, D. and Hyndman, D., 2000, Roadside Geology or Northern and Central California,Mountain Press, Missoula, MT.
Bailey, E., W. Irwin, D. Jones, 1964, Franciscan and Related Rocks, Bulletin 183, CA Division of Mines and Geology.
Elder, W., Geology of the Golden Gate Headlands, National Park Service, Golden Gate National Recreation Area, PDF file: geology/geoguide.pdf
Konigsmark, T., 1998, Geologic Trips, San Francisco and the Bay Area, GeoPress, Guala, CA.
McPherson, G., Phipps, S. and Grossman, J., 1990, Diverse Sources for Igneous Blocks in Franciscan Melanges, California Coast Ranges: Journal of Geology, v. 98, p. 845-862.
Maruyama, S., Liou, J. and Seno, 1989, Possible Depth Limit of Underplating by a Seamount: Tectonophysics, v. 160, p. 327-339.
Pestrong, Raymond, Professor, Geology, San Francisco State University, e-mail exchange.
Seiders, V., 1991, Conglomerate Stratigraphy and Tectonics in the Franciscan Assemblage of Northern California and Implications for Cordilleran Tectonics: U. S. Geological Survey Open File Report, OFR 91-50, 21 p.
Schlocker, J, 1974, Geology of the San Francisco North Quadrangle, California, Geologic Survey Professional Paper, 782, Washington D.C.
Wahrhaftig, C., 1984, A Streetcar to Subduction, American Geophysical Union, Washington, D.C.
Wakabayashi, J., 1992a, Nappes, Tectonics of Oblique Plate Convergence and Metamorphic Evolution related to 140 Million Years of Continuous Subduction, Franciscan Complex: Californian Journal of Geology, v. 100, p. 19-40.
Wakabayashi, J., 1992b, Metamorphism and Tectonic Origin of Franciscan Metabasites and a Field Trip Guide to Three Localities in the San Francisco Bay Area, in Schiffman, P., D. Wagner, ed., Field Guide to the Geology and Metamorphism of the Franciscan Complex and Western Metamorphic Belt of Northern California, California Division of Mines and Geology, Special Publication 114.
Wakabayashi, J., 1999, The Franciscan Complex, San Francisco Bay Area: A Record of Subduction Complex Processes in Wagner, D., Graham, S., ed., Geologic Field Trips in Northern California, California Division of Mines and Geology, Special Publication 119.


The geologic map and section on this sheet were compiled and interpreted from several different maps and related research:
California Division of Mines and Geology, Geologic Map of the San Francisco-San Jose Quadrangle, California, 1:250,000, Map 5A, Regional Geologic Map series.
Wahrhaftig, C., A Streetcar to Subduction, American Geophysical Union, Washington, D.C.,1984, several different maps and diagrams.
USGS Topographic Map, San Francisco Quadrangle, 1:100,000 series, 1978.
USGS Geologic Map of the San Francisco North Quadrangle, San Francisco and Marin Counties, California, Plate I, Professional Paper 782, 1974.


Protogaea Civica II (Franciscan Formation/San Francisco, CA ) was completed for the San Francisco Civic Center in conjunction with the opening of the new De Young Museum in San Francisco in the Fall of 2005.

Protogaea Civica III (Santa Rosa) was commissioned in 2006 by the Sonoma County Museum of Art.