Last summer I shared a picture of the similar Spot-winged Glider (Pantala hymenaea) washed up on the beach. If you'd like to compare, you can review the post from 10 July 2014.
While we experience a short heat wave today and tomorrow (over 100°F or 38°C in Santa Rosa today!), I wouldn't be surprised to see more migrant dragonflies appearing in our area.
P.S. We don't know what happens to these dragonflies. Do they fly too far offshore and run out of energy? Do they get blown out to sea by strong winds?