Katydid

Hi Katie, If you don't know or are unsure of the ID please tick the "Help me ID this species" box so others know to ID it for you. I agree with Goody's ID suggestion. A good reference for you in your area is http://nathistoc.bio.uci.edu/ Many of your spottings may be in here.

Nice spotting. This is actually a planthopper, and my best guess is the species suggested above, which has been introduced to California from Australia. Take a look and see if it matches up for you.