Figures 4, 10, 11b, 11c. San Andres “C” waterflood unit. (4) Structure map on top of the San Andres Reservoir. (10) Net pay isopach map of the “A₁” zone tidal channels, (11b) net pay isopach map of “A₂” subzone, (11c) net pay isopach map of “A₃” subzone.