Geologic Hazards and Disasters Research Group

Supplemental Table 3. Stratigraphic unit descriptions for Trench T3.

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

300 QTP5Y 7/3 Light grey pale yellow
Pebbly sandy clayey silt. Interbedded, well-sorted fine-medium sand with massive pebbly sandy silts and silts. Highly fractured in SW half of its exposure. Strongly cemented by gypsum in fractured zone. Somewhat less indurated near the top. Contains filament sand nodules in upper portion. Pebbles are clustered in places. Rock types include granite, dark mafic crystalline rocks, Monterey Formation derived laminated mudstone (Dibblee, 1973), and quartz.
310 A) 2.5Y 7/4 Pale yellow
Cobble-pebble sandy silt. Well indurated, massive. Fractured along NE side. Clasts are predominantly crytaline and the granotoids are deeply weathered to grus. Subangular to subrounded small cobbles. Well cemented by gypsum and CaCO3. Some steeply dipping tectonic fabric.
B) 2.5Y 7/3 Pale yellow
Interbedded highly fractured well-indurated fine sand, silt and subangular to subrounded pebbly coarse sand. Beds are approximately 10 to 20 cm thick. Silt and mudstone are finely laminated to massive. Pebbly zones are mostly clast-supported. Upper portion is less indurated and may have been weathered. May grade into 310 below. Appears to mostly be a coherent block.
C) 2.5Y 7/3 Pale yellow
Massive, bedded, well-indurated silt and fine sand. Bedding is a few cm think. One zone of pebbles is evident on 1993 log. Top appears to have been sculpted and then buried by 320. Pervasively sheared in most places.
320 Sandy silt well bedded with gravel lenses incised into it. CaCO3 nodules along the top.
330 2.5Y 7/3 Pale Yellow
Clayey very fine sand silt. Mostly massive and densely bioturbated. Coarse sand to pebble sized clasts distributed throughout. Few CaCO3/gypsum blebs (white). Sheared at base. Numerous CaCO3/gypsum filaments in upper portion. Contains numerous QTP clasts. Some are dismembered and soft (weathered) while others are still well indurated. South-west of trench color change 2.5Y 5/2 light olive brown.
340 2.5Y 6/4 Light yellow brown
Similar to 330, darker in color. Fewer CaCO3/gypsum blebs/filaments. Small sandy pieces possibly from burrows. Higher percent of coarse sand and pebbles than 330, but may grade into 340.
3502.5Y 6/4-3 Light yellowish brown
Relict and real bedding in places, massive in others. Upper contact is gradational with 370. Angular poorly sorted very coarse to fine sand lenses and stringers interbedded with laminated and crossbedded silt and very fine angular pebble gravel.
360 Massive clayey-pebbly sandy silt. Chaotic distribution of clasts. Well bioturbated. Gradational boundary with 330.
3702.5Y 6/4 Light yellowish brown
Big scour with angular very coarse sand with fine to large pebble clasts. Very fine sand and coarse silt, 3 to 5 cm interbeds with gravel lenses and stringers (coarse sand to fine pebble with occasional small pebble clasts). Mostly subangular with occasional subrounded clasts. Patchy uncommon CaCO3 coating and blebs (white) and filaments. Poorly sorted overall. Bimodal sand/silt and gravels. Fine scour-and-fill structures. Clasts: granite, meta sediments, quartz, feldspar, and gypsum crystals.