Hundreds of miles from Arizona's most famous chasm (bottom), another grand canyon lies beneath the ocean off Northern California.
Shown "drained," the canyon network under Monterey Bay
(digital illustration at top) is every bit as complex--and, at approximately 300 miles (480 kilometers) long and a mile (1.6 kilometers) deep, nearly as big--as the Grand Canyon
But unlike the Grand Canyon--known to have been carved by the Colorado River--Monterey Canyon is still a new frontier. Only now are the mysteries of its formation being illuminated, via cutting-edge submersibles and core samples, according to the August 2009 documentary Drain the Ocean
on the National Geographic Channel.
One emerging theory: Driven by waves, underwater avalanches of sand and gravel carve the cliff faces.
Also see: Drain the Ocean interactive map >>
Illustration and photograph courtesy Burning Gold Productions via National Geographic Channel