Cannabis in California has been legal for medical use since 1996, and for recreational use since late 2016. The state of California has been at the forefront of efforts to liberalize cannabis laws in the United States, beginning in 1972 with the nation's first ballot initiative attempting to legalize cannabis. Although it was unsuccessful, California would later become the first state to legalize medical cannabis with the passage of the “Compassionate Use Act” of 1996. In November 2016, California voters approved the “Adult Use of Marijuana Act” to legalize the recreational use of cannabis. As a result of recreational legalization, local governments (city and county) may not prohibit adults from growing, using, or transporting marijuana for personal use. Following recreational legalization, existing growers and suppliers of medical cannabis were required to register, comply with regulations, and apply for permits. Many existing growers have been slow to apply for permits as it has been estimated that 60 percent or more of all cannabis consumed in the United States comes from northern California.
You can read more about California laws in Department of Public Health and the Department of Cannabis.

Recreational Cannabis Laws in california

Immediately upon certification of the November 2016 ballot results, adults age 21 or older were allowed to:

Possess, transport, process, purchase, obtain, or give away, without any compensation whatsoever, no more than one ounce of dry cannabis or eight grams concentrated cannabis to adults the age of 21 or older.
Possess, plant, cultivate, harvest, dry, or process no more than six live plants and the produce of those plants in a private residence, in a locked area not seen from normal view, in compliance with all local ordinances.
Smoke or ingest cannabis.
Possess, transport, purchase, obtain, use, manufacture, or give away marijuana paraphernalia to peoples the age of 21 or older.

Users may not:

Smoke it where tobacco is prohibited.
Possess, ingest or smoke within 1,000 feet (300 m) of a day care, school, or youth center while children are present (except within a private residence and if said smoke is not detectable to said children).
Manufacture concentrated cannabis using a volatile solvent without a license under Chapter 3.5 of Division 8 or Division 10 of the Business and Professions Code.
Possess an open container or marijuana paraphernalia while in the driver or passenger seat of a vehicle used for transportation.
Smoke or ingest marijuana while operating a vehicle used for transportation.
Smoke or ingest marijuana while riding in the passenger seat or compartment of a vehicle.

Medicinal cannabis

If you have a physician’s recommendation to use cannabis, you can:

Buy cannabis products with more THC
Buy more cannabis at a time, if needed for your medical condition
Possess more cannabis
Grow more plants at home, if needed for your medical condition
Get a medical marijuana ID card
Even with a physician’s recommendation, you must follow laws about where you can use cannabis.

Eligible medical conditions

Your primary care physician can recommend cannabis to help you manage any of these medical conditions:

Acquired immune deficiency syndrome (AIDS)
Anorexia
Arthritis
Cachexia (wasting syndrome)
Cancer
Chronic pain
Glaucoma
Migraine
Severe nausea
Persistent muscle spasms (for example, spasms caused by multiple sclerosis)
Seizures (for example, epileptic seizures)

Your physician can also recommend cannabis to help with chronic or persistent medical symptoms that either:

Substantially limit your ability to conduct major life activities
May cause serious harm to your safety, physical health or mental health