Fray Mariano Francisco de los Dolores y Viana, of the College of Santa Cruz de Querétaro, came to Texas in 1733 and by 1734 had made the acquaintance of all the principal Indian tribes along the Brazos River. In the summer of 1736 he participated in a controversy between priests and soldiers over the San Antonio River bridge, and in 1740 he addressed a strong representation to the viceroy against an order for the payment of tithes. As early as 1745 he was advocating the establishment of a mission on the San Xavier (San Gabriel) River and in 1746 began work at the site where San Francisco Xavier de Horcasitas Mission was formally established in 1748. Although Fray Mariano's actual assignment was that of minister of San Antonio de Valero Mission, he was active in the establishment of several missions, the San Xavier Missions being his special interest. After the founding of the other two missions, Nuestra Señora de la Candelaria and San Ildefonso, and San Francisco Xavier de Gigedo Presidio, trouble between the soldiers and the Indians caused Fray Mariano to recommend the removal of the presidio and the establishment of a civil settlement. His defense of the missions, in spite of recommendations for their removal, caused trouble with Governor Pedro del Barrio Junco y Espriella and his successor, Jacinto de Barrios y Jáuregui. After the murder of one of the friars, Pedro de Rábago y Terán ordered the removal of the missions to the San Marcos River; but he had no authority to do so, and the missions were shortly abandoned and the neophytes asked to join the San Antonio missions. For those who did not want to go to San Antonio, Fray Mariano established the mission of San Francisco Xavier in 1756. Dolores remained president of the four Queretaran missions until 1773, when they became the responsibility of the Zacatecan missionaries.