To Mexico from California, ID required?

My friends and I wanted to go to Mexico from California, but we weren't sure about the ID we would need. None of us are from California and didn't bring our passports or birth certificates when we came to visit. Would we be able to cross the border with a driver's license and several other forms of ID? Or is a passport/birth certificate necessary?

[Rolly]

It depends on were you want to go. If it's just TJ and the near-by beaches, you'll have no problem at all. Going deeper into Mexico, could be a bit of a hassle. Going back to the USA may get you some questions, but they will let you back in so long as you are walking or driving. Going or returning by plane probably will not work.

[BajaGringo]

Rolly is correct. As long as you have US ID in the form of driver's license, etc you shouldn't have a problem unless you speak with a heavy foreign accent and driving a vehicle with non-US plates...