This study centers on the impact of migration on the vitality of San Lucas Quiaviní Zapotec (SLQZ) spoken in the Central Valleys of Oaxaca, Mexico. The data show (a) that children in Los Angeles, whether US- or Mexican-born, are not growing up as active SLQZ speakers and (b) that given sustained travel between the two communities, language use in Los Angeles is replicated in San Lucas, thereby introducing Spanish and English into otherwise Zapotec-only domains such as the home. The case of SLQZ is one in which a language vitality assessment that considers the home community only, would lead to an incorrect evaluation. Signs of language endangerment become evident in a sociolinguistic analysis that crosses borders.