The central portion of San Luis Potosí State, Mexico, contains many isolated basic alkalic volcanic centers of Quaternary age, including seven large maar complexes. These vents are divided into two geographically distinct groups, Ventura to the southwest and Santo Domingo to the northeast. The maars and other volcanic centers contain xenoliths of mantle‐derived spinel lherzolite and lower‐crustal granulites. The Santo Domingo maars also contain kaersutite megacrysts derived from kaersutite‐rich veins in spinel lherzolite. Basic volcanic rocks form a well‐defined petrologic series from strongly silica‐undersaturated olivine nephelinites and basanites rich in spinel‐lherzolite xenoliths and xenocrysts which, are dominant at Ventura, through alkali olivine basalts and basalts having little to no lherzolitic debris, which are dominant at Santo Domingo. All rocks have olivine phenocrysts with Cr‐Al spinel inclusions, titanaugite‐augite phenocrysts or microphenocrysts, and groundmass crystals of one or both Fe‐Ti oxide series. Plagioclase decreases in abundance with increasing normative ne + lc and is absent or restricted to the groundmass in the most undersaturated rocks. Normative ne + lc is also strongly correlated with the abundances of incompatible elements, among which the degree of enrichment in the suite decreases in the sequence Nb, Ta, P, La, Th, Ce, Sm, Sr, Ba, Zr, Eu, Hf, K, Ti, Yb, and Na. Based on experimental analogs and major and trace element abundances, the entire volcanic suite from San Luis Potosí can be modeled by progressive degrees of partial melting of a garnet peridotite mantle source. In this scheme, the Santo Domingo magmas were produced by relatively larger degrees of partial melting. Equally plausible, however, is formation of the San Luis Potosí magmas as mixtures of melts from two different mantle sources. In this scenario, the Ventura‐type mantle is enriched in Nb, Ta, P, La, and related elements compared with the Santo Domingo‐type mantle. In Pier et al. [this issue] we describe Sr and Nd isotopic data for these samples that demand multisource models.