The dotted lines next to Angel Island denote the outbound traffic lane for deep draft vessels. The smaller dotted lines to the right denote the inbound deep draft vessel lane for ships going to Richmond Long Wharf, Sacramento and Stockton. Bouys are shown on a chart by the purple tear-shaped marks you see around the traffic lanes (the white areas). This bouy is probably the one just above the 47 foot sounding. This is just an educated guess based on the background in the picture.