Geologic Hazards and Disasters Research Group

Supplemental Table 2. Stratigraphic unit descriptions for Trench T2.

Noriega, et al. Stream Channel Offset and Late Holocene Slip Rate of the San Andreas Fault at the Van Matre Ranch Site, Carrizo Plain, California

200 QTP5Y 7/3 Light gray pale yellow
Paso Robles Fm. Medium coarse, well indurated, clayey, fine, sandy silt. Sub-angular to sub-rounded sand and pebble lenses, coarsening upward overall. Bedding parallel faults along silt-clay bedding planes. Coarsens upward into poorly to well sorted fine-medium sands. Also contains angular pebble stringers (poorly sorted)--coarse sand to medium pebbles (average is fine pebble). Medium bedded (5-20 cm) sands and gravels with massive units (>20cm). Some fining upward packages. Crude fine bedding in some sands and gravels. Some gypsum accumulations near upper contact. CaCO3 cemented.
210 5Y 7/2 Light gray
Mudstone, fine sandstone and matrix supported pebbles. Approximately 15 cm thick with approximately 3 cm gradation to upper unit. Disappears towards bottom. Lower in mobile upper portion of QTP (Dibblee, 1973). Alternative contact for QTP at top. Thinly bedded, inclined toward paleochannel. Derived locally from QTP below and upslope.
Upper 5Y 7-6/4 Pale yellow-Pale olive
Massive clayey silty pebbly sand. Very friable. Gypsum and CaCO3 filaments and cement. Occasional pebble and sand lenses- possibly relict bedding ( 4-5 cm thick, 12-14 cm long). Contains occasional clasts of QTP. Sharp contact at base in lower portion with QTP.
2205Y 7-6/4 Pale yellow- pale olive
Angular pebble-gravels towards base with cut in fill structures. Grades upward into coarse to fine sand. Poorly sorted. Some discontinuous silty laminae are present. Not as well organized as 250 (likely bioturbation). Grades laterally into 230 and 240. Clasts are granite (dominates), metasediments, feldspar, coarse gray sandstone, hard mudstone, quartz, mafic crystalline rocks.
2305Y 7/3 Pale yellow
Fine sandy silt, with clay and pebbles. Lateral gradation to SE from 220. Massive, structureless, likely bioturbated. Some gypsum with CaCO3 filaments disseminated
2405Y 7/3 Pale yellow
Fine sandy silt, with clay and pebbles. Lateral gradation to NW from 220. Structureless, likely bioturbated. Base is olive sandy silt grading upwards from QTP.
2505 Y 7/3 Pale yellow
Sub-angular to sub-rounded poorly sorted grains; quartz, feldspar, mafics, granite pebbles, metasediments. Laminated silts: some planar, some dipping or trough shaped. Coarse angular sand lenses. Fine to medium sand lenses. Shallow scour-and-fill structures (3 cm high). Basal coarse pebble sand with coarse materials in the center. Few small lenses of fine-pebble subangular clast supported. Occasional angular cobbles towards top, but overall unit is less bedded upwards, and shows more colluvial input upwards
2605Y 6/3 Pale olive
Medium-coarse pebbly sandy silt. Pockets of predominantly QTP-derived clasts approximately 5-10 cm in diameter. Structureless debris flow or slope wash. No filaments. Does react with HCl. Includes some gypsum blebs.
2705 Y 7/3 Pale yellow
Very fine, densely bioturbated, structureless, clayey sandy silt. Rooted, slightly more organic towards the top. At base has some pebbles. Fewer random clasts than 260.