In Spanish Alta California, most agricultural production was under the management and on the lands of the Franciscan Missions, operated with native labor. Each of the four presidios (forts) was also supposed to rely on a ranch belonging to the King -- the Ranchos del Rey. Monterey's corresponding royal ranch, for example, was located upriver, somewhat near the Missions of Soledad and San Juan Bautista. Who staffed or managed these royal ranchos?
Presidio soldiers were appointed to manage the ranchos (Life in Presidial California by Lothrop and Herczog). Sargeant Miguel Espinosa was in charge of the King's Ranch of Monterey (Memorias sobre la historia de California by Amador).
Without doubt, the bulk of the field labor was done by natives; whether they were Mission neophytes on leave, or exempt from missionization, I don't know.