Which formation consists of graywacke and inter-bedded shale?

The Franciscan Formation is known for its complex geological composition, which includes a significant presence of graywacke and inter-bedded shale. Graywacke is a type of sandstone characterized by its coarse-grained texture and is often associated with tectonic settings where sediments are rapidly deposited, such as in subduction zones. This formation reflects the tectonic history and sedimentary processes active in California during the Mesozoic era, particularly related to the subduction of oceanic plates beneath the North American Plate.

Inter-bedded shale within the Franciscan Formation indicates a history of alternating depositional environments, where finer sediments, like shale, were laid down in calmer conditions compared to the more turbulent conditions responsible for the graywacke deposition. This unique combination illustrates the dynamic geological history of the region, attributable to its location along tectonic boundaries.

Other formations listed, such as the Monterey Formation, are primarily known for their rich fossil content and biogenic limestone, the Los Angeles Basin represents a more modern sedimentary environment, and Pelona Schist is primarily composed of metamorphic rocks, which do not typically include graywacke or shale in significant forms. This distinction reinforces the identifying characteristics of the Franciscan Formation as the correct answer.