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Figure 6. (a) Lithologic log of northeast wall of trench T2 (see Fig. 5 for location). Several nested channels are cut into the local Paso Robles bedrock unit. The channels are filled with clast- supported gravel that grade outward or are cut into and overlain by colluvial units or channel deposits that have been pedogenically altered. The lowermost channel thalweg (base of unit 210) is the match for the offset thalwegs exposed in T6', T8, and T7. The explanation indicates the patterns, line types, and labels used in all of the logs. (b) Lithologic log of the northwest wall of trench T3 (see Fig. 5 for location). This trench exposed three main shear zones that progressively cut up section from southwest to northeast. Gray-green unit 300 is correlative with unit 200 from trench T2 (Fig. 6a) and is juxtaposed against highly sheared and deformed tan Paso Robles or older Quaternary units to the southwest. Units 370 and 375 represent the channel fill sequence. The two channel fill packages are separated by a fissure fill unit that probably formed in the 1857 earthquake. See the trench log explanation in Figure 6a. (c) Lithologic log of the southwest wall of trench T6 (see supplemental Fig. 1a, available in the electronic supplement to this article, for the northeast wall and Fig. 5 for location). Clast-supported sand and gravel fluvial deposits fill nested channels cut at the base into local Plio-Quaternary bedrock (units 610 and 630). The base of unit 640 is the thalweg offset from the exposures in trench T2. Importantly, ¹⁴C sample T6'-4 dates the colluvium into which the channel was cut, providing a maximum channel age. See the trench log explanation in Figure 6a. (d) Lithologic log of the northeast wall of trench T8 (see supplemental Fig. 7b, available in the electronic supplement to this article, for the southwest wall and Fig. 5 for location). Clast-supported sand and gravel fluvial deposits fill nested channels cut at the base into local Plio-Quaternary bedrock (units 810 and 830). The base of unit 840 is the thalweg offset from the exposures in trench T2. Most of the ¹⁴C samples in this study come from the top of unit 860 and provide a minimum channel age. See the trench log explanation in Figure 6a. (e) Lithologic log of the northeast wall of trench T7 (see supplemental Fig. 7c, available in the electronic supplement to this article, for the southwest wall and Fig. 5 for location). Because of its older age, the stratigraphic relationships are more obscured than the younger trenches by pedogenesis. Nonetheless, unit 730 has eroded into the local bedrock (a Quaternary fan deposit) and its base represents the thalweg that we correlate with that exposed in trenches T2, T6', and T8. This channel thalweg is offset about 48.8 m. See the trench log explanation in Figure 6a.

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