In the study of emerging varieties of Spanish in the United States, the Tijuana-San Diego border area presents a unique opportunity for the study of language contact in that English and two varieties of Spanish (U.S. and Mexico) are in constant contact with one another. In the San Diego area we find two types of Spanish native speakers, corresponding to two generations: a heritage group that is English-dominant and an immigrant group that is Spanish-dominant. Tijuana speakers represent monolingual controls that are the closest point of reference, linguistically and demographically, to immigrant and heritage speakers in San Diego. In a fieldwork study of 22 families (11 on each side of the border) that consists of naturalistic spoken data in a conversational setting, I focus on two linguistic features of Border Spanish: the use of the subjunctive and the use of fillers. With respect to the subjunctive, heritage speakers exhibit an attenuation of the imperfect subjunctive in optional contexts and an increase of the imperfect subjunctive outside of subjunctive contexts.

I propose that this difference is due to a unique mode of heritage acquisition of Spanish wherein heritage speakers begin their acquisition of English through formal schooling at the same time that nuances of the subjunctive are still being acquired. The onset of English education and gradual shift to English dominance may result in reduced input in Spanish that prevents heritage speakers from fine-tuning their use of the subjunctive in certain contexts, leading to the observed effects. With respect to fillers, heritage speakers complement their system of Spanish fillers with English fillers. In spite of not being English dominant, some immigrant speakers begin to use English fillers with limited functions when compared to heritage speakers. These indirect transfer effects in the use of fillers may be due to San Diego speakers’ highly-variable exposure and interactions in both Spanish and English. Whereas heritage speakers may transfer the filler 'so' directly from English, immigrant speakers' transfer may be the result of interaction both with heritage speakers and exposure to English. This dissertation explores the role that acquisition and transfer effects play in contact-induced language change in the Spanish spoken in San Diego.