Ghost island off San Francisco
July 12th, 2006I have always been intrigued by ancient islands now drowned under the waves by rising seas.
I was looking at the lovely new Geology of the San Francisco Bay Region, a guidebook by Doris Sloan, and noticed such an island about 20 miles off Point Reyes, northwest of the city.
Between 18,000 and 14,000 years ago, the rising ocean cut off a hill on the coastal plain, forming an island. Animals would have become stranded there, and over the next few thousand years some might have begun to evolve in their isolation. But the island continued to shrink, and by 11,500 years ago had been reduced to a few small islets. They submerged by 10,500 years ago, and the life of the place came to an end.
The remains of the island can still be seen, as Cordell Bank, where divers swim amidst the pinnacles that were the last remains of the island before it was gone.
[geology]