Health and Safety Code 11357 HS is the California marijuana law that sets forth the rules for personal possession of marijuana for recreational purposes. Possession of not more than 28.5 grams of marijuana (a bit more than an ounce) for personal use is legal in California as of January 1, 2018, for people age 21 and older. So is the possession of up to eight (8) grams of concentrated cannabis (hashish).