If one wants to do the coast, do yourself a favor and do it in OR or WA.
CA's campgrounds and parks are falling apart, dirty, unmaintained, super expensive and just the worst in North America (haven't tried Mexico's, so perhaps an exaggeration). I was showing my friends the coast last week and we couldn't wait to cross the border to OR. Yuck; a real embarassment.
BTW, it was 80F+ when I took the photo below: sometimes anytime but summer is the best time to go.