Steaming in at High Tide
On the California coast the Pacific Ocean rises and falls twice a day. Funneling through the Golden Gate, the rising tide fans out eight miles to the farthest parts of the Bay where it piles up in the narrower and shallower areas. Therefore the Bay's surface is never level. A boat passing under the bridge at high tide and reaching the southern end of the Bay two hours later would travel uphill four feet. By which time the tide at the bridge might have begun to ebb and the difference in the elevations might be as much as seven feet.

A high tide passing under the bridge will reach Alcatraz in ten minutes, the Ferry Building twenty minutes later, and Richmond ten minutes after that. Finally the delta port of Stockton will receive that same high tide six and a half hours after it passed the Golden Gate. Conversely, one sixth of the Bay flows out of the Golden Gate on the ebb tide. As the tide reverses itself every six hours, its flow accelerates from zero at slack water to a maximum tide crest of 4,600,000 second-feet, which is about seven times the flow of the Mississippi River at its mouth.
[ MAP B-7 ]