The Post-glacial Flooding of San Francisco Bay,
animation and map images


At the time of the last glacial maximum, about 18,000 years ago, global sea level was about 130 meters lower than it is at present. Between 18,000 and about 6000 years ago, most of the ice melted off of Canada and Scandinavia, causing sea level to rise, flooding the rims of all the dry lands.

At the glacial maximum, the central Californian coastline near lay near the edge of the continental shelf, outboard of the Farallon Islands ridge. San Francisco bay and its related waterways were dry-land river valleys. As sea level rose during the glacial meltdown, the coast gradually moved inland, across the shelf and into the bay. The sea extended well into California's central valley but was then filled in to form the Sacramento/San Joaquin delta and estuary.

To view this movie, click on the image.


Download: Flooding of San Francisco Bay Movie + jpg images (24 MB).


Note that, in addition to the movie, the download package includes the images for the present shorelines and for those of 1890. It is quite interesting to click back and forth between these two maps, noting the manmade changes that have occurred in the interval. 1890 was the oldest detailed map I could locate. If you know of an older one, especially one of the delta, I'd love to see it and to incorporate it into this package, if allowed. One from earlier than 1849, when the gold diggers began to send their debris down the rivers, would be really exciting to see.

Created by Tanya Atwater using Photoshop and Morph, following maps and information from K. R. LaJoie, U.S.G.S., and Brian F. Atwater, U.S.G.S. and U Washington, as presented by Doris Sloan, U.C. Berkeley.


Comments on this and all of the materials offered on this site are welcomed: atwater@geol.ucsb.edu