The Migrating Delta

The Delta is a relatively recent geological feature rather than an ancient one. Fourteen thousand years ago, the glacier-covered Sierra Nevada stood above a landscape where the San Joaquin and Sacramento Rivers joined and flowed swiftly through riverside forests and grassy plains, but there were no islands, sloughs, quiet backwaters, or Delta here. With much of the earth's water locked in glaciers and polar ice caps, sea level was three hundred fifty feet lower than today, the Pacific Coast lay thirty miles west of the present shoreline, and today's bay did not exist. The river instead continued out the Golden Gate and deposited sediment into a vast coastal delta. As the earth warmed, ice melted, and sea level rose, that older coastal delta was flooded, newer deltas formed and were flooded farther and farther upstream, and only six thousand to eight thousand years ago did the Delta settle in its present location, earning the nickname the Inland Coast.

Oakley, California · United States