• East view from Crissy Field overlook with old Coast Guard station on left and city on right

    Presidio of San Francisco

    California

Mélange

Mélange at the coastal bluffs

Large blocks in the mélange at the coastal bluffs include green serpentinite and basalt in the foreground, graywacke sandstone in the background, and bedded red chert in between.

Will Elder, NPS

Mélange is a mashed-up mixture of rocks, mixed and crushed in a subduction zone. Zones of mélange lie between large areas (miles across) of more coherent rocks of similar type (called terranes) that form larger-scale mixture of rocks that is the Franciscan Complex. Smaller blocks of oceanic crust and sediments and continental marine rocks are mixed together in the mélange and encased in extremely sheared rock that is typically altered to clay.

Did You Know?