Green’s Dictionary of Slang

(US Mex. teen) a white person.

1970		J. Wambaugh New Centurions 3: That‘s just like a Texas Chicano [...] Afraid I‘ll disgrace him in front of the gabachos.
1993		L. Rodríguez Always Running (1996) 185: ‘The gabachos on Marshall Street tried to jump me, an,’ [...] ‘Fuck ’em [...] Let’s get them white boys’.