The article deals with the issues of intervariant dialectology of Spanish. The form of existence of Spanish in the territory of southwest states of the United States of America is defined as Mexican territorial dialect of the Spanish language outside of Mexico; its national and cultural specific features are described. The paper constitutes the fact that Mexican territorial dialect of Spanish outside of Mexico is highly diverse and exhibits a wide array of variation regionally, ethnically and socially. Variation in Spanish of the United States is due to the results of a founder effect, later immigration from across the Spanish diaspora and sociolinguistic variables such as ethnicity, socioeconomic status, age and gender.