Can we use a California drivers license and birth certificate to reenter the state from a day trip to mexico?

yes you can use unless you pass the Baja California then you need a passport

The answer is yes.. I've done many times.. now I have a passport..

You are supposed to have a passport or border crossing card. Using this I.D system greatly enhances our border security because state I.D. are easier to fake. Please, help keep our borders secure and use a passport.