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Flat Point

USGS Topo Sheet: Shaw Island

Geographic coordinates: 48°32.95' N, 122°55.02' W

Paleoseismic record: Insufficient fieldwork has been completed to evaluate the paleoseismic potential of this site.

Setting: Flat Point is a spit that encloses a relatively undisturbed freshwater marsh behind 1-to-2-m-high beach berms on its northeast and west sides. A 120-m-long pond has developed behind the berms next to a hillslope.

Stratigraphic description: Three gouge cores (2.5 cm diameter) from near the middle of the marsh showed 20 cm of sandy peat over clean sand. Rigg (1958, p. 162) noted that none of the 35 salt marshes he visited in the San Juan Islands contained peat deposits >1 m thick.

Paleontology/Paleoecology: No paleontologic work has been completed.

Geologic interpretation: The freshwater marsh appears to be developed on low (<1 m high) beach berms, sandy tidal flats, and/or dunes. Although peaty sediment beneath the marsh is apparently thin (<0.3 m thick), peaty sediment near the pond may be thicker. If so, this site may hold some potential for preserving a record of prehistoric coseismic land-level changes, tsunamis, or storms.

Date of last work at site: September 1997

Status of work: No additional work is planned.

Published information on this site: None

Investigators: H. Kelsey, A. Nelson

Please use the following format in citing information from this page:

Kelsey, H.M., Nelson, A.R., Flat Point, in Bucknam, R.C., compiler, 1999, Atlas of reconnaissance data from paleoseismic studies in the Puget Sound region, Washington: U.S. Geological Survey Web Page, http://earthquake.usgs.gov/regional/pacnw/paleo/atlas.html.

This URL is: http://earthquake.usgs.gov/regional/pacnw/paleo/reports/flatpt.htm
Modified July 29, 2002 by Susan Rhea