I definitely agree with Rich and Bryan that you should get certified at home. California water is cold but I’m sure there are great instructors in your area. Your instructor will make sure you are dressed appropriately and stay warm. (Some people even learn to dive in a drysuit during open water classes.) The added benefit is that you will also establish a relationship with local dive instructors and you will know who to go to when you are ready to advance in your skills and education. I also agree that a certification is not something you want to rush.
You will also want to learn in local conditions since that is where you will be diving most often. Since you are near cold water, any trip to the tropics will be a treat. I learned to dive in Oklahoma and that made me get used to low vis and hone my navigation skills. As a result, I am super-appreciative when the vis is 15+ ft. I had another acquaintance who learned to dive in Okinawa and was completly spoiled. He is jaded about most dives now.
If you still decide to get certified on vacation, check on the class size before you commit. Sometimes, larger resorts=larger classes. If you do go for a rush job, make sure you at least get individualized attention. I recently dove with Aquamarine Divers in Speyside, Tobago and they are a small and meticulous operation. (The location is remote but worth it.) I also like Southpoint Divers in Key West. I’ve seen how both shops do business and you would be okay to get certified by them.