Hi Brian I am assuming you are referring to the Algodones border. Personally I would pay extra for an expedited passport card or book however if you truly want to take a chance carry as much ID as you possibly can however I would not advise it Hope that helps a little.
Sorry Brian, I don't know since I have been carrying my passport for years and don't want the hassle that I see other people have at borders and flights.
The US border agents are at the crossing. I would stop there before entering Mexico to be certain there are minimal issues returning.
Take your I'd and a birth certificate
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