These are Sea Gooseberries (Pleurobrachia bachei). Various sizes were represented, but most individuals were ~1-1.5 cm across.
Here are two different views from above:
Although most of the gelatinous animals in these aggregations were comb jellies, every now and then a hydromedusa would appear. In the image below, look for the individual that's larger with lots of short tentacles around the rim, and small red dots (barely visible) at the base of the tentacles.
The hydromedusa is Polyorchis penicillatus. To see a picture of one swimming in Tomales Bay last November, click here.
I'm not sure exactly why so many comb jellies and hydromedusae were washing ashore, but it may have been related to strong winds.
P.S. If you're new to the blog and would like to learn more about Sea Gooseberries, review earlier posts from 15 July 2013 and 19 February 2012.