Why are the chert beds so bent and folded?
Many Franciscan chert beds are highly folded and contorted, but within a short distance they often appear to be unfolded. Some scientists believe that this type of folding is the product of the slumping of the soft gelatinous silica-rich sediments, contorting them before they are fully hardened into rock. This slumping may have occurred on the flank of an oceanic mountain range as earthquakes shook the tectonically active mid-ocean ridge. Another theory is that the chert beds were folded by compressive forces developed as the Franciscan Complex was created by the scraping and addition of oceanic rocks to the western margin of North America.
