Between Berkeley and Angel Island there are two deep draft vessel traffic lanes (dredged areas where big ships can navigate safely, without running aground). We go round the one nearest to Angel Island a lot because sea lions are usually sunbathing there and the kids (and adults) onboard our boat love to see them. Judging from the background, this is that bouy.
If anyone wants to see it for themselves, we are taking our boat to Angel Island on Sunday from 9:00 - 3:00. Freepmail me.