This all happened in late 1751.
The viceroy instructed the Captain to restore the soldiers of the existing garrison to their respective areas and to enlist 50 men and voluntary settlers.
The missionaries were also to secure settlers for the area. The Real Presidio de San Xavier was to be built on a site chosen by the captain and the missionaries.
The presidio was to be a formal fortification built for the garrison with similar defenses around the chapel, which was to have a small square.
The location was not necessarily permanent, but could be moved if required.
After Captain Rabago y Teran made an inspection of the missions in December, 1751, he and Father Mariano, the missionaries of the three missions, the soldiers from the garrison, the brick mason and carpenter began exploring the river for a place to establish the presidio and the village.
"(We)...traveled up river to a district called Apache Pass at which point they crossed the river and not having seen a site which suited them or which suited their plans, and having come down river, arrived at a high hill near the river with a good view in all directions."
They all came to agreement that the San Francisco Xavier de Gigedo Presidio should be erected on it because of the nearness of water, since although the river was at some distance, there was a lagoon near by which the Reverend Fathers said was full all year.
There was sufficient water for mortar as well as for the necessities of the house.
After Rabago examined the map and drawings he conferred with all those standing around and confirmed the presidio had sufficient space conforming to the needs of the plans.