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New data from marine dredgings off Monterey, California, correlated with wells and outcrops on land, indicate that the Pleistocene Monterey and Soquel Canyons, and the middle Miocene (?) Carmel Canyon, are intimately related to the continental geologic history.
Late Cretaceous (?), middle Miocene, and Pleistocene structure controls canyon trends whereas the induration and distribution of post-lower Miocene sedimentary rocks and the Cretaceous granodiorites control the canyon-shape parameters. Carmel Canyon was the principal canyon until the mid-Pleistocene orogeny caused physiographic and structural changes. Zones of low induration and (or) weakness along fault trends and along contacts between sedimentary and igneous rocks permitted the canyons to be more easily eroded.
Late late Miocene, Pliocene, and early Pleistocene drainage from the Great Valley debouched at Monterey Bay via Elkhorn Slough which lies at the head of Monterey Canyon. All canyon heads were cut or modified subaerially by rivers to a depth of 300 ft. below present sea-level during eustatic sea-level changes. Canyon erosion below 300 ft. was by submarine processes, as the geologic record on land indicates no great uplift of the ocean floor.
Monterey Canyon and Elkhorn Slough lie directly above a buried middle Miocene canyon--the Pajaro Gorge. The older canyon is not ancestral to Monterey Canyon, but cause-and-effect relationships are noted.
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