No passport

I'm in SD visiting from NM. I forgot my passport. I've heard you can sweet tall your way across (both ways) w/out one. Is this true? Any advice (other than bring it next time)?

I plan on crossing on foot at San Ysidro

I think your SOL!. However if you have your SS with you it could work. I also have a passport card that I carry woth me all th3 time. It will only work with Mexico and Canada but does the trick and I just keep it like my DL.