Cordell Bank National Marine Sanctuary, Marine sanctuary on continental shelf, California.

Cordell Bank National Marine Sanctuary protects 1,286 sq mi (3,331 km2) of ocean about 50 miles (80 km) northwest of San Francisco. Its core is a granite seamount, part of the Sierra Nevada 93 million years ago, whose upper pinnacles rise to within 115 ft (35 m) of the surface above an average depth of 400 ft (122 m). The reef face is crusted with pink encrusting organisms and pale sponges, with a dark rounded fish beside a ruffled sponge patch.

Cordell Bank was discovered in 1853 by George Davidson of the U.S. Coast Survey during a mapping expedition. In 1869 Edward Cordell located the shoal west of Point Reyes by following birds and marine mammals, then measured depth with a lead weight. Robert Schmieder's Cordell Expeditions documented the bank from 1978 to 1986, leading to its designation as a sanctuary on May 24, 1989.

The bank's name comes from Edward Cordell, who in 1869 located the shoal west of Point Reyes by following flocks of birds and marine mammals, then measured depth with a lead weight on a line. From 1978 to 1986 the non-profit Cordell Expeditions, led by Robert Schmieder, made scores of dives there and published a monograph in 1991; that work led to sanctuary status.

The bank lies about 50 miles (80 km) northwest of San Francisco, with its upper pinnacles reaching within 115 feet (35 m) of the surface and an average depth of 400 feet (122 m). Recreational SCUBA diving is not recommended because of the depth and currents. Late summer is the best time to see migrating whales feeding on the krill that gathers near the bank.

Cordell Bank was once part of the Sierra Nevada and has been carried about 3 cm north each year by plate movement along the San Andreas Fault. During the last ice age, when sea level was 110 m lower, it stood as an island. The granite seamount now rises to within 35 m of the surface.