Recently published name change for the asexual species in California: Haploembia solieri is now called Haploembia tarsalis. The third photo is of a nymph.
The sexual embiid Haplo solieri retains it's name and the population is spreading around Santa Clara County. The information is from J. S. Edgerly.
This is the first webspinner I've seen! Kinda cool. Going by this comment on BugGuide and pics elsewhere on the web, I'm guessing this is Haploembia solieri, mostly due to the faint spots on the back of the head. Apparently it's not native to CA. Boo.