José Francisco Mariano Garza was a Franciscan priest at Bucareli, a town founded in 1774 on the Trinity River. From its inception, the settlement was plagued by an unhealthful environment and periodic flooding. Beginning in May 1778 it was threatened by Comanche attacks on livestock. In January 1779 Garza reported on rapidly deteriorating conditions. Residents dared not hunt except in large, well-armed numbers, but doing so would leave the town vulnerable to attack. The final blow was a devastating flood that struck in February, followed by renewed Comanche attacks. The settlers then abandoned Bucareli and moved to the site of present Nacogdoches. Garza transferred church ornaments and sacred vessels to the site of the abandoned mission of Nuestra Señora de Guadalupe de los Nacogdoches. He later defended the move to Governor Domingo Cabello y Robles, arguing that the area around Nacogdoches had a healthier climate and was situated near friendly Tejas Indians. Nacogdoches became a permanent haven for the settlers, and it seems likely that Garza continued to minister to his parishioners there.
Garza later returned to New Spain, and in January 1791 he met with Father Manuel Julio de Silva in Coahuila to plan a new missionary field among the northern tribes. At San Antonio the padres learned that they could not move through Apache territory without a military escort, which was denied them, so they redirected their efforts toward founding a new mission among the coastal Karankawas. The undertaking was approved, and in February 1793 Garza opened Nuestra Señora del Refugio Mission at the junction of the San Antonio and Guadalupe rivers. He did not remain long at the new mission, however. Suffering from the unhealthful coastal climate, Garza asked permission to retire to Zacatecas in September 1793. Upon approval of the request, Silva left Texas and died within a few months at his missionary college.