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GT-6 (Figure 5) there are a few (less than 5) feet of unweathered fine-grained sediment (silt) directly beneath the basal contact of the channel This unweathered section is underlain by a few feet of weathered sediment that is interpreted as a paleosol (see below for paleosol descriptions) The unweathered sediment is absent beneath the axis of the main channel (GT-10 in Figure 3 and GT-4 and GT-11, Figure 4) It is also absent beneath the secondary channel in GT-18 (not shown, see Appendix A) and near the bifurcation point of the two channels in GT-16(Figure 4) The data from GT-16, GT-18, and GT-20 also force revisions in the isopach map for the 1St Riverbank aquifer (Figure 7) Previously we estimated thicknesses of 19 feet, 7 feet, and >20 feet for these wells,respectively The thickness was less in both GT-16 and GT-20 and greater in GT-18 than expected This creates two isopach "thicks" representing channel axes, rather than-the single axis previously postulated One axis trends north-south through GT-6 and GT-17 and the other trends more to the southeast from GT-18 through GT-5 and GT-11 The two appear to merge just east of GT-14 Hence, the Ist Riverbank channel appears to have been braided, with an interchannel bar of finer-grained sediment trending from GT-12 through GT-1 The channels are shown most clearly in Figure 5, which trends transverse to the channels in an east-west direction Figure 3 trends in a more north-south direction through the interchannel area before crossing the main channel near GT-I Note that in that well, the channel is incised into an older paleosol, whereas in the interchannel area it is less deeply incised into unweathered sediment of the I"Riverbank Aquitard Where even more deeply incised, the 1St Riverbank Channel may have eroded through the I" Riverbank Aquitard,into the underlying 2nd Riverbank Channel (aquifer), as shown in Figure 5 near GT-6 The boring log for GT-18 (Appendix A) provides a good example of this, as well as a complete description of the material filling the western branch of the channel The sand coarsens downward from fine-to-coarse-grained at 60 feet to medium-to-very coarse-grained at 65 feet, and then to at least 10 feet of more poorly sorted, clayey sand that contains small pebbles We interpret the poorly sorted clayey-pebbly sand as a channel lag deposit at the base of the channel This lag deposit records erosion of the underlying silty clay bed that separates the I" and 2nd Riverbank channel deposits However, the silty clay bed was not encountered in GT-18, and the I St Riverbank channel sand lies directly on the 2"d Riverbank channel deposit The sand-on-sand contact occurs between the clayey-pebbly sand at 75 feet and the fine-to-medium-grained sand that lacks clay at 80 feet The three new wells that penetrated the 2"d Riverbank aquifer (GT-16, GT-17, and GT-18) yielded thickness data 'that match earlier predictions well Therefore, only minor modification of the isopach map for this aquifer was required (Figure 8) Only one main channel has been identified in this interval, trending mostly north-south until bending to the west between GT-I and GT-3 Figure 4 parallels the channel just to the north of the axis and shows that the thickness remains relatively constant from GT-20,to GT-11, but then increases rapidly as the section crosses the axis at GT-3 before thinning on the south flank of the channel in CPT-4 The base of the channel was not reached in GT-3 but we postulate that the channel eroded through the unweathered upper portion of the 2"d Riverbank aquitard into the underlying paleosol, which was penetrated in both GT-11 and GT-15 at a depth of between 100 and 105 feet,just below the bottom of GT-3 • 4