The Golden Gate

Stand on the bluffs at Lands End and look north. About a mile of moving water separates San Francisco from the Marin Headlands, and every tide pushes the Pacific in or pulls the Bay back out through this one gap. It is the only door between the Bay and the ocean.

It was not always the door. For hundreds of thousands of years, the rivers draining into the Bay’s valley left by a different route, south through a low gap near what is now Colma. Then the San Andreas Fault did what it always does and moved the land sideways. Somewhere between 75,000 and 130,000 years ago, the southern tip of the Point Reyes Peninsula slid far enough northwest to uncover a notch in the bedrock. The water found it. Geologists today call that notch the Golden Gate.

During the last ice age there was no bay at all. The ocean stood far lower, and the Sacramento and San Joaquin rivers ran through the Golden Gate in a valley and on toward a coastline well to the west of today’s.

When the ice melted, the sea came back. It reached the Golden Gate between 10,000 and 11,000 years ago and poured into the valley behind it, spreading across low ground as fast as 30 meters a year. Around 8,000 years ago the rise began to slow, and by 6,000 years ago it was about a tenth as fast. The valley had become a bay.

The people who lived beside the strait were the Ohlone, to the south, and the Coast Miwok, to the north. Ohlone villages stood where Crissy Field and Fort Mason are now.

Europeans were slow to find the gap. A Spanish land expedition under Gaspar de Portolá first saw the Bay in 1769, and on August 5, 1775, Juan Manuel de Ayala brought the supply ship San Carlos through the strait, the first known ship to sail in. The name came more than seventy years later, from the American explorer John C. Frémont, who called it Chrysopylae: the Golden Gate, after the Golden Horn of Byzantium. It was never about gold.