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i above and coated the ped surfaces The clay skins are smooth, shiny, and sometimes slickensided Soil peds may be associated with fractures, formed by shrinkage and expansion of the sediment during soil formation, and the fractures may be filled with the white precipitate discussed above The development of clay skins implies more thorough and long-lived soil formation Additional features that have been observed in the palsosol horizons include tiny holes and bits of plant fragments These are inferred to be evidence of rooting and plant growth during soil formation Neither of these features is common in unweathered sediment Whether paleosols can be detected on CPT logs is presently uncertain Direct evidence (color, soil peds, fracture fillings, and plant fragments) is not obtainable from these logs, but degree of lithification is a feature that might be identifiable In many, if not most cases, however, this is masked by the greater differences caused by grain size For example, the log for CPT-1 (Figure 4) clearly identifies the 1St Riverbank Aquitard-2"d Riverbank Aquifer-2"d Riverbank Aquitaid sequence between 70 and 90 feet The evidence from the nearby auger borings proves that a thick paleosol has formed over all of these units Distinguishing this paleosol from the underlying unweathered portion of the 2nd Riverbank Aquitard, however, is problematic in CPT-1 No specific log features are obvious Most of the paleosols formed on fine-grained sediment that was deposited between channel- forming intervals Examples are the soil that overlies the 3td Riverbank Channel (evident in all three cross sections) and the soil that underlies the Modesto Channel The latter does not appear to affected the underling 1St Riverbank Channel to a significant degree, but the former extends � downwrd into the 3rd Riverbank Channel in GT-11, GT-12B, and GT-15 Hence, it is thicker and implies a longer period of soil formation j I The thickest and best-developed paleosol underlies the lSi Riverbank Channel and extends downward through the 2nd Riverbank Channel into the underlying 2"d Riverbank Aquitard, at least locally (e g Figure 4) Only the basal (deepest) portion of the 2"d Riverbank Channel does not appear weathered in GT-3, according to the boring log prepared by Richesin and Associates This is supported by the log of GT-1213, the lower few feet of pebbly sand in this boring become clayey and browner upward, and more than 50 blows were needed to collect a 6-inch sample of the brown sand r In most cases, palsosols are either parallel or subparallel to bedding, but Figure 4 shows an interesting exception A reddish-brown paleosol was encountered from 50 to 55 feet in GT-20, sandwiched between gray or brownish-gray unweathered sediment Forty feet to the west, the sediment at this depth consisted of gray to gray-brown silt in GT-16 However, reddish-brown, black, and white veins and relict plant fragments were observed 10 feet above this Similar features were observed at 55-60 feet in GT-8 Thus, this paleosol apparently arches upward from GT-20 to GT-16 and then back down at GT-S, revealing the presence of an ancient hill This paleotopography likely influenced the location of the Modesto Channel, which diverted around the hill and preferentially stabilized in the flatter terrain south of the hill (note that the paleosol is relatively flat- lying south of GT-11 in Figure 4 and to the west in Figure 5) 6