Franciscan Complex

Franciscan Complex
Stratigraphic range: Late Jurassic to Late Cretaceous
Chevron folds in ribbon chert of the Marin Headlands, California. Geologist Christie Rowe for scale.
Type	varied; primarily metamorphic (low grade), but also sedimentary, igneous and high-pressure metamorphic
Underlies	various
Overlies	basement; Coast Range Ophiolite in some areas
Lithology
Primary	schist (incl. serpentinite), sandstone, basalt, greywackes
Other	shale, chert
Location
Region	California Coast Ranges, northern Transverse Ranges
Country	United States
Type section
Named for	San Francisco, California

The Franciscan Complex or Franciscan Assemblage is a geologic term for a late Mesozoic terrane of heterogeneous rocks found throughout the California Coast Ranges, and particularly on the San Francisco Peninsula. It was named by geologist Andrew Lawson, who also named the San Andreas fault that defines the western extent of the assemblage.^[1]

The Franciscan Complex is dominated by greywacke sandstones, shales and conglomerates which have experienced low-grade metamorphism.  Other important lithologies include chert, basalt, limestone, serpentinite, and high-pressure, low-temperature metabasites (blueschists and eclogites) and meta-limestones. Fossils like radiolaria are found in chert beds of the Franciscan Complex. These fossils have been used to provide age constraints on the different terranes that constitute the Franciscan. The mining opportunities within the Franciscan are restricted to deposits of cinnabar and limestone.

The outcrops of the formation have a very large range, extending from Douglas County, Oregon to Santa Barbara County, California.^[2] Franciscan-like formations may be as far south as Santa Catalina Island. The formation lends its name to the term describing high-pressure regional metamorphic facies, the Franciscan facies series.^[3]