Juan José de Ganzabal, a missionary priest in Spanish Texas, was assigned to the College of Santa Cruz de Querétaro, a Franciscan institution in Mexico. He and Father Mariano Francisco de los Dolores y Viana were staunch advocates of the San Xavier missions, on the San Gabriel River near the site of present Rockdale, Texas. It fell to Father Ganzabal to make special pleadings with the auditor de guerra for crown support of the missions and a presidio to guard them. That task occupied him in Mexico City for eight months in 1748. Despite opposition in Texas from Governor Pedro del Barrio Junco y Espriella, by July 1749 three missions had been established on the San Gabriel River. Ganzabal was the first regular missionary at San Ildefonso Mission, where he directed his initial efforts toward the recruitment of several bands of Orcoquiza Indians. In May 1750 a horrible smallpox epidemic spread through neophytes of the mission, and Father Ganzabal could do little other than minister to the needs of the dying.
After the establishment of San Francisco Xavier de Gigedo Presidio in 1751 and appointment of Capt. Felipe de Rábago y Terán as its commander, the status of the missions deteriorated rapidly under the influence of the roguish captain. When matters came to a head over an adulterous affair between Rábago and the wife of soldier Juan José Ceballos and the immoral conduct of the garrison, Ganzabal delivered Father Miguel de Pinilla's decree of excommunication and posted it at the gate of the presidio. But within a few days, Ganzabal granted absolution and penance to the repentant soldiers.
Matters, however, continued to worsen at the San Gabriel outposts. On May 11, 1752, Ceballos and Ganzabal died, respectively, of gunshot and arrow wounds at Nuestra Señora de la Candelaria Mission. The attack was almost certainly instigated by Rábago but was blamed on Coco Indians. Ganzabal was one of only a few Franciscans to suffer violent death in Texas. His murder stands alone as the extreme expression of marred relations between the missionary clergy and presidial soldiers on the frontier of Spain in America.