The head and lower jaw are covered with knobs called tubercles, which are actually hair follicles and are characteristic of the species.

The whale, first spotted at Oakland's Outer Harbor October 10, 1985,[6] swam up the Carquinez Strait, the Sacramento River and under the Rio Vista Bridge to a dead-end slough 69 miles (111 kilometers) from the ocean.

Pless and his colleague Dale Galarowicz quickly gained Navy permission and rushed the equipment to Rio Vista where Humphrey was last seen.

Early the next morning, the equipment was loaded onto the private yacht, Boot Legger, loaned by its owner for the rescue effort.

As they approached the San Francisco Bay and the water gained in salinity, Humphrey became visibly excited and began sounding.

Though the crew lost sight of him that night, they picked him back up in the morning and led him out through the Golden Gate Bridge into the Pacific Ocean on November 4, 1985, at 4:36 p.m.[9] The town of Rio Vista later erected a commemorative granite marker at City Hall at the east end of Main Street.

[11] Humphrey stayed a considerable time in 1990 in the embayment immediately north of Sierra Point in Brisbane where occupants of the Dakin Building could observe his antics.

Humphrey became beached on a mudflat in San Francisco Bay to the north of Sierra Point and to the south of Candlestick Park.

Researchers Louis Herman and Bernie Krause led a team of scientists who used sound recordings of natural whale feeding vocalizations to guide Humphrey back to safety.