California's San Antonio water system was definitely used into the 20th
    century by cattle ranches in the area.  It may have also been used in
    part during the 19th century for some placer mining done in this part
    of central California.  Francis Rand Smith's book on the
    above-mentioned Spanish mission discusses some of these later uses, as
    does the Historic Preservation Plan for Hunter Liggett prepared by
    BioSystems with the able assistance of Julia Costello.  Original
    elements of the system remain undisturbed in some areas, other locales
    have been reconfigured, cemented, and altered.
 
    By the way, there was also a study done recently on the aqueduct
    leading from the San Diego Mission Dam to the Mission.  Check with the
    archeological clearinghouse in that area.
 
    Leo