San Francisco was an ancient river valley were creatures who grazed and browsed and stalked their prey, left their bones. (text on the horizontal surface) There Is Nothing On Earth Exactly Like The Fog Of San Francisco Bay...
20,000 years ago you could have walked to the Farallon Islands...
When the sea was more than 300 feet below its present level, a marshy delta extended to the coastline 30 miles west, past the Farallon Islands. The great basin that would hold San Francisco Bay evolved from a valley carved by an ancient river carrying torrential runoffs from the uplifted granite range of the Sierra, long before Sacramento or San Joaquin had been so named. Creating the straits we call Carquinez, the river scoured the rugged valley floor to grind its way to the ocean. On the valley floor, smaller spring-fed streams cut between upthrust rocky points and ridges; thousands of years later Spanish explorers name them: Alcatraz, home of pelicans; Yerba Buena, a fragrant good-tasting herb; and Tiburon, shaped like a shark.
Dwellers of the Ancient Valley...
The cooler, wetter climate was more like that of the northwest California today. Thick forests of oak, pine, and fir covered the slopes of the western hills, and stands of redwood filled the narrow valleys - home to deer, bear, giant ground sloth, mastodon, and wolf. In the great valley trough, bison, antelope, camel, horse, mammoth, and mastodon grazed and browsed across grasslands where saber-tooth cats and dire wolfs stalked their prey. Waterfowl filled the wetlands; walrus and barking sea lions basked on offshore rocks. As centuries passed many animals were trapped and buried in bogs, marshes, and seasonal floods, leaving their bones as fossil records of a world that vanished with the melting of the ice sheets, the rising of the sea-level, and the coming of humans.
The Landscape of the Valley Floor...
The course of the ancient Sacramento River turned south as it met the last line of western hills (now the eastern shore of Marin), flowing into the northern end of the great natural trough that would become San Francisco Bay. The river ran in a deep narrow valley close to these steep western hills, and broke through this last barrier at a gap that we call the Golden Gate. Free of the hills, the river crossed a broad, low coastal plain to empty into the sea near the surf-pounded granite cliffs - now the Farallon Islands. Low rolling grasslands covered the floor of the great trough with more hills rising beyond. A few wooded hills rose above the bunch-grasses like islands, and moving in between, murmuring streams bordered by alders, and willows wound lazily through to join the ancient river.
Legend Told of a Great Shaking of the Earth...
Mountains split, sea water rushed in, filling the ancient valley to make a vast inland bay. Geological truth is more complex. About 15,000 years ago, as the earth warmed, the glaciers of the world began to melt. The level of the sea began to rise, and over the next 10,000 years ocean waters gradually drowned the immense inland valley of the ancient river. Filling first the deepest canyons of the great river, the sea crept up until it reached a point 381 feet above the river's bedrock at the narrow entrance to the bay. By possibly 10,000 B.C., invading salt water had moved through the Berkeley Hills at Carquinez Canyon and spread to the lowlands of the Central Valley. San Francisco Bay was of age, ready for the coming of man.
In most of the earth, fog is a dark, disagreeable smudge that comes from
nowhere...In San Francisco the fog is a thing of beauty and wonder, a daily drama of the elements
with the wide bay as the central stage. It is the mystery of imagined happenings,
the suspected drama of half-seen coming and goings, of ships and shadows and men moving
like ghosts in the billows. Like the bay itself, our fog is born of the violent meeting of land
and sea at the place where the ocean breached the western mountain barrier and invaded the
continent's edge. It is conceived out of the cold oceanic deeps and the fertile heat
of the Central Valley. It is shaped and given substance by the rotations of the planet and the
drift of the currents and the flowing rivers of atmosphere."