Does my dog need a passport to immigrate to the United States?
It may be easier for dogs or cats to immigrate to the United States than for humans. They do not need passports. There are, however, requirements that their owners must follow in order to bring them to the U.S. 
The importation of animals, in general, is regulated by the Centers for Disease Control and Prevention ("CDC"). There are different rules depending on the type of animal that is being imported into the United States. In addition to the CDC's regulations, each state and airline may have additional rules. This post will discuss the requirements for bringing your dog or cat into the United States.
Dogs
A general certificate of health is not required by CDC for entry of pet dogs into the United States, although some airlines or states may require them. (California does not.) Pet dogs are subject to inspection at ports of entry and may be denied entry into the United States if they have evidence of an infectious disease that can be transmitted to humans. If a dog appears to be ill, further examination by a licensed veterinarian at the owner's expense might be required at the port of entry.
Proof of Rabies Vaccination:
Dogs must have a certificate showing that they have been vaccinated against rabies at least 30 days prior to entry into the United States.
Importation of Unvacinated Dogs:
Dogs not accompanied by proof of rabies vaccination, including those that are too young to be vaccinated (i.e., less than 3 months of age), may be admitted if the importer completes a confinement agreement (see below) and confines the animal until it is considered adequately vaccinated against rabies (the vaccine is not considered effective until 30 days after the date of vaccination).
Puppies that are too young to be vaccinated (i.e. less than 3 months of age) must be kept in confinement until they are old enough to be vaccinated, and then confined for at least 30 days after the date of vaccination.
Unvaccinated dogs must be vaccinated within 4 days of arrival at their final U.S. destination and within 10 days of entry into the United States, and must be kept in confinement for at least 30 days after the date of vaccination.
Dogs may not be sold or transferred to other owners during this period of confinement, and the person that signs the confinement agreement is responsible for ensuring the conditions of the agreement are met.
Importers must provide a contact address where the dog will be kept during the confinement period. If the importer will be housing the dog at several addresses or traveling with the animal, all points of contact must be provided.
Cats
A general certificate of health is not required by CDC for entry of pet cats into the United States, although some airlines or states may require them. (California does not.) Pet cats are subject to inspection at ports of entry and may be denied entry into the United States if they have evidence of an infectious disease that can be transmitted to humans. If a cat appears to be ill, further examination by a licensed veterinarian at the owner's expense might be required at the port of entry.
Cats are not required to have proof of rabies vaccination for importation into the United States. However, some states require vaccination of cats for rabies. (California does not require it.)
The CDC maintains quarantine stations at the major ports of entry throughout the United States. In San Francisco, the CDC's station is located at the San Francisco International Airport, International Arrival, Terminal G - Second Level, Federal Inspections Area, San Francisco, CA 94128. Their phone number is (650) 876-2872. This is a list of all the stations.
CDC's website is very comprehensive and discusses the requirements for all sorts of animals: monkeys, rabbits, birds, etc. You should consult it when making your departure plans. Although California does not have specific requirements for dogs and cats, they do have rules for other animals. You may find more information on the website for the California Department of Food and Agriculture. Finally, you should consult the specific airline you will be taking as to their requirements for transporting your pet. The major airlines have this information on their websites.
