He was born circa 1680.
He got lost when traveling alone between Mission Candela and Coahuila (Monclova), a distance of 20 leagues, being very short-sighted. After eight days, his father-in-law and sons-in-law went out and spent four days looking for him, at the behest of the governor, but they couldn't find Castro's trail because it had been overrun by herds of wild horses. They concluded he must be dead, since the land in that area was very sterile and "infested" with hostile Indians. The governor himself (Joseph Antonio de Ecay y Muzquiz) went out to search with a company of Tlaxcaltecs and other friendly Indians, but finding some of his possessions, they also thought he must be dead, since he was a man of "little experience and knowledge of the area". A year later Juan Galvan Alvarez de Godoy petitioned to marry Josefa Valdez, Castro's wife, but the petition was denied. (Marriage investigation of Juan Galvan Alvarez de Godoy and Josefa Valdez, 1717)
He died in 1716 in Candela . He was 36 years old.