Originally Posted by
Steve M
There really is no entry control. I have crossed into Mexico on foot at the Tijuana border crossing several times. It's simply a matter of two sets of one-way turnstiles, no more formal than exiting a zoo. There is one point where Mexican Customs has an officer stationed there that can pull people aside for a Customs inspection, but virtually nobody is pulled aside. And, there is zero in terms of Immigration inspection. It's not just a matter of them not stamping your passport - nobody checks anyone's passport at all.
Though probably not at the time of the OP's crossing, but the above is no longer true at the Tijuana/San Ysidro crossing into Mexico. They actually do have a real building now. Gone are the days of the disinterested customs officers watching the turnstiles. There is now a dedicated pedestrian entry building, staffed by Mexican immigration officials, in which you do have to present a passport (or Passport card) and get a cursory interview by immigration. If you presented a passport they stamp it, if a card, they don't. Then you go to a red/green randomizer for customs, but they'll let you bypass it if it is obvious you're not carrying anything.
It surprised me the first time I crossed it last October after many years of not crossing. I'd estimate it's still less than a year old.
I did ask once for a non-US citizen friend considering a day trip to Tijuana, and it was recommended to drop off the I-94 (if they had one) at the US CBP office before crossing (and to pick up a new blank one).
Edit: I don't know if that would have worked. He decided against the day-trip.