You can read the law itself below though you will gain better context by reading this conversation on Beer Advocate.
CA Growler Label Requirements:
ABC – label (even if handwritten) must be approved by ABC – send to Diana Villanueva, diana. [email protected], (916) 419-2571.
Name of manufacturer
City, State of manufacturer
Net contents (TTB requirement)
ABV if over 5.7%
Government Warning label (TTB requirement) :
(1) According to the Surgeon General, women should not drink alcoholic beverages during pregnancy because of the risk of birth defects.
(2) Consumption of alcoholic beverages impairs your ability to drive a car or operate machinery, and may cause health problems.
To be considered a growler, in CA, must have a sealed container (distinguished from a glass of beer) – doesn’t matter how you seal it – screw cap is fine.
To be a growler under TTB, must fill prior to sale.