The orginal indigenous inhabitants of the area around Momax, Zacatecas
were Caxcanes, Tepecanos and perhaps Zacatecas. All of these ethnic
groups were Uto-Aztecan speakers, meaning that the languages that they
spoke were related to Nahuatl, though Tepecano is not as closely related
to the others. The migration of that group southward was much later
than that of the Mexica, and is closer to Pima and some Southwestern
U.S. indigenous languages. Uto-Aztecan speakers are originally from the
area around Arizona and Utah (thus the Uto in the language family name).
But you are correct in that the names are Nahuatl-derived. Soon after
Spanish arrival in the area, the local indigenous populations were
largely decimated and other natives migrated to the area to meet labor
needs. I know that in Colotlan, Jalisco, hundreds of Tlaxcaltec
families were brought in as colonizers by the Spanish and "mexicano"
(the language of the Mexica and Tlaxcaltecs now academically refered to
as Nahuatl) was the lingua franca by the early 1600s. It seems that
many of the names were Nahuatlized.