Set your alarm: March 1 is the day to reserve Labor Day weekend campsites in California.
Campsite reservations for California state parks, including campsites at the always popular Monterey beaches, Santa Cruz Mountains and Sierra Nevada, open up at 8 a.m. on March 1. Those reservations cover Labor Day weekend and beyond (and any summer sites that are still available).
http://m.sfgate.com/outdoors/article/book-labor-day-campsites-california-10966871.php