It is interesting that outside of Chevrolet and GMC none of the GM brands show up in the top 10.
From:
Market share of top-selling auto brands in California in the second quarter
Toyota: 23.4%
Honda: 12.4%
Ford: 9.6%
Chevrolet: 8.2%
Nissan: 7.0%
Mercedes-Benz: 3.7%
BMW: 3.7%
Lexus: 3.6%
Dodge: 3.6%
GMC: 2.6%
Source: California Motor Car Dealers Assn.