Wanderlust World Wanderlust World From the Mesozoic to the Miocene, the Farallon Plate subducted beneath the North American Plate, driving the formation of the Coast Ranges through multiple mechanisms:
Convergence generated intense horizontal compression, buckling crust into folds (anticlines/synclines) and thrust faults.
Scraped-off oceanic sediments, basalt, and chert were plastered onto the continental margin, building the Franciscan Complex—a chaotic mélange forming much of the Coast Ranges' core.
Accreted material thickened the crust; buoyancy forces lifted the ranges.
Flux melting above the slab produced volcanic arcs (now eroded plutons like the Salinian Block granites).
Uplift exposed deep crustal rocks; rivers carved the modern topography.
Today, the San Andreas transform system has replaced subduction, but the Coast Ranges' architecture is a fossil record of that ancient convergence.