In an nutshell, to return to California only dogs, not cats, require a rabies certification. Health certificates are not required for either dogs or cats.
As information can change, below are some of the regulations with links to find the latest information:
Federal level: According to the CDC, all dogs and cats must appear healthy on arrival. The CDC does not require rabies certificates if the dog is coming from Mexico. They state as an example: "Your adult dog lived in the United States and visited Mexico. This dog does NOT require a rabies certificate or CDC Dog Import Permit, because Mexico is NOT on the list of high-risk countries for dog rabies." View more federal information about bringing dogs and cats.
State level: The USDA has a handy tool to check state requirements to import a pet. Scroll down to "Additional State Requirements" and select the U.S. state you will be crossing into from Mexico. For example, for California, the CDFA states:
Dogs: "All domestic dogs must be healthy. Dogs over four (4) months of age must have documentation proving current rabies vaccination. A Certificate of Veterinary Inspection (CVI), also known as a health certificate, is not required for privately owned dogs entering California. Dogs imported into California for the purpose of being sold or changing ownership require a health certificate issued by a licensed and accredited veterinarian within 10 days prior to importation."
Cats: "All domestic cats must be healthy. Neither a Certificate of Veterinary Inspection (CVI), also known as a health certificate, nor a rabies vaccination is required to import a cat into California. (Does not apply for plane travel)."
Consider bringing proof of pet ownership with you as it may come in handy.