California Code, Business and Professions Code - BPC § 25240

(a) Any wine labeled with a viticultural area appellation of origin established pursuant to Part 9 (commencing with Section 9.1) of Title 27 of the Code of Federal Regulations, other than the viticultural area “Napa Valley,” and which is located entirely within a county of the 29th class, shall bear the designation “Napa Valley” on the label in direct conjunction therewith in a type size not smaller than 1mm less than that of the viticultural area designation provided neither designation is smaller than 2mm on containers of more than 187ml or smaller than 1mm on containers of 187ml or less.  This requirement shall apply to all wines bottled on or after January 1, 1990.

(b) The department may suspend or revoke the license of any person who violates this section.

(c) This section shall not apply to any wine labeled with a viticultural area appellation of origin established pursuant to Part 9 (commencing with Section 9.1) of Title 27 of the Code of Federal Regulations when the name of the appellation includes the term “Napa Valley.”