Franciscan Complex

The Franciscan Complex is a diverse group of rocks formed along California's Pacific coast, mainly during the late Jurassic to early Cretaceous periods (about 150 million years ago). It originated in a deep ocean environment where sediments, volcanic materials, and oceanic crust were scraped off and accumulated onto the edge of a tectonic plate. Over time, these materials were buried, compressed, and transformed into complex, challenging rocks like greywacke, shale, chert, and serpentinite. This complex represents a history of subduction and plate movements, making it a key feature in understanding the geology of California's coast.