Supplemental Table 7. Stratigraphic unit descriptions for Trench T9.

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

910
2.5Y 7/3 Pale yellow
Older alluvial fan unit with steeply dipping beds of indurated silt, silty sand and silty sandy gravel. Beds are subparallel to the trench and undulate so that the exposure on the NE wall shows “windows” of different beds and apparent dips. Several “caves” formed in both walls along bedding plane failures. Attitude on a siltstone bed at the SE end of the trench is N35W 70°SW. Exposures of silty sandy gravel, and silty sand or sandy gravelly silt. Maximum clasts size is 22 cm. Many clasts have well developed rinds of carbonate or gypsum. Coarse plutonic clasts have grusified. Crystal roses of gypsum and “spaghetti worms” (2-5 mm) of gypsum are scattered, but concentrated in some places. Clasts are mostly well rounded ranging to subrounded or subangular, clasts are dominantly coarse and fine crystalline rocks.
920 2.5Y 7/4 Pale yellow
Sandy gravel and silty sandy gravel lenses and small channels with sharp, scoured contacts in a matrix of gravelly silty fine to coarse sand with pebble stringers. Several small channels have fining upward sequence of granule to fine sand. Scattered specks (2-5 mm) of chalky white minerals could be gypsum or calcite. Maximum measured clast size is 12 cm. Dominant clast lithology is igneous (felsic and mafic, primarily plutonic with some volcanic). Foliated metamorphic, and quartz rich clasts also present. Most clasts are well rounded, 20 to 40% are angular. Most clasts do not have mineral coatings or rinds.The upper contact with unit 930 is sharply defined by color change. The upper edges of the channel are gradational with unit 910.
930 2.5Y 6/4 Light yellowish brown
Massive silty gravelly sand to silty coarse sand with abundant rootlets, roots and poorly defined suspected infilled burrows. This unit extends to the ground surface. A well-defined scoured channel is filled with stratified coarse sand and pebbles, grading upward to pebbly sandy silt and pebbly sand, near the SE end of the trench, visible on both walls. The upper part of the small channel may be bioturbated and is gradational with the rest of the unit.

Valid HTML 4.01 Transitional