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The area between the Mexican border, and the nearest checkpoint in the United States.

Its called that because this area is inhabited by Mexicans. (close to 85%) Since there are a lot of Mexicans, there are a lot of Mexican heritage in the area making some areas look and feel like Mexico, and also at times speak border language.(i.e Tex-Mex)
"Hey man where are we? There's a lot more Mexicans then white people."
"We past the checkpoint in Falfuras. We're now in Pre-Mexico"
by w12w34 December 03, 2013