Many mid-to-late 19th century (circa 1850s thru 1880s) descendants of families whom resided in areas such as: Huejúcar, Jalisco State; Guadalajara, Jalisco State; Nochistlán, Zacatecas State; Delicias, Chihuahua State; Calvillo, Aguascalientes State and Victoria de Durango, Durango State -- have ancestral origins within the Midi-Pyrénées region of France and/or North Western region of Spain near the Bay of Biscay.
It's believed (circa 1878 thru 1880) that the Southern Pacific may have employed former "Ferrocarril Central Mexicano" Mexican Central Railway employees in its effort to bolster the newly formed "Southern Pacific of Mexico" endeavor (however, research continues into this theory).
It would appear that in later years (circa 1898 thru 1909) Southern Pacific took an approach of purchasing former Mexican Railway operations to expand its operations in support of early economic interests in the area. Thus, several former employees of Mexican Railway operations found opportunities in the US during this timeframe.
Specifically, most French Basques (of the aforementioned Mexican states) took up residence within various hub towns -- e.g., the 1880 hub town of Maley in Pima County, Arizona - which in 1881 became Cochise County; and, then in 1889 the town of "Maley" was renamed Willcox.