None of the cities in Silicon Valley have bans or restrictions on specific dog breeds. However, even though these cities don't forbid certain breeds, know that many landlords and property managers will, so owning a pitbull, rottweiler, doberman pinscher or other breed frequently maligned in the media can make it harder to find a home. Those that do allow pets may charge an additional deposit.
You should always license your pet. If you live within Santa Clara county you can find instructions on how to do this at their county website. San Mateo county requires licensing for dogs and recommends it for cats. You can find instructions on licensing your pet online, by mail, or in person on their county website.
Dogs and horses must be registered with the city each year by law. Online registration is available at the Los Angeles Animal Services website.
One of the great things about this part of California is that the great outdoors are so accessible -- no matter where you live you won't be far from nature. However, the hills and mountains around the Valley are home to rattlesnakes.
Bites do happen here, particularly in the spring after snakes have emerged from hibernation. For your dog, this is incredibly painful and can be deadly. And for you, this can be incredibly upsetting and expensive: a single vial of anti-venom is $500. When you're out walking with your dog in the mountains make sure you keep your dog on the leash and keep an eye on where your dog is sticking its nose. Rattlesnakes don't always rattle when you approach, and baby snakes don't even have a rattle, so you won't always know you're near one.
As an added precaution, you can enroll your pooch in rattlesnake aversion training. For about $100 your dog will be trained to avoid these snakes based on sight, smell, and sound.
Helpful Pet Resources
Pet Restrictions: What to know before you relocate your pet overseas.
?What you need to know on relocating your pet abroad.