No. 39: May-Jun 1985
"The first detailed views of vast stretches of the seafloor in U.S. coastal waters have revealed features so immense and unexpected that they defy the imaginations of the scientists who discovered them." A special sonar device named Gloria is being employed to produce high resolution maps of the seafloor. Apparently previous sonar sounding methods missed startling underwater volcanos, canyons, and immense delta-like deposits. About 170 miles off San Francisco, near a huge volcanic structure, Gloria discovered an underwater canyon comparable in size to the Grand Canyon. No one really knows how it was formed. This great chasm is associated with a delta-like deposit twice the area of Massachusetts. Normally, one expects alluvial fans at the ends of canyons, but in this instance the submarine canyon actually cuts down into the fan. Where such a huge mass of material came from is a mystery rivaling that of the canyon's origin.
(Yulsman, Tom; "Mapping the Sea Floor," Science Digest, 93:32, May 1985.)
Reference. The geological puzzles presented by submarine canyons are detailed in ETV1 in our Catalog: Carolina Bays, Mima Mounds. For a description of this book, visit: here.