Preliminary Geologic Map of Bainbridge Island, Washington

Bainbridge Island is in the center of the Puget Lowland, Washington, surrounded
by the waters of Puget Sound. Winslow, the commercial center of the island, is
a 35-minute ferry ride from Seattle. The island lies within the Suquamish and
Bremerton East 7.5-minute quadrangles. This open-file report is an advance view
of quadrangle-format mapping of these areas by the U.S. Geological Survey.

This study of Bainbridge Island was undertaken in response to (1) recent
awareness of the hazard posed by future earthquakes in the Seattle fault zone,
at the south edge of the island, and the need to marshal geologic evidence for
the rate and style of deformation; (2) increasing population on Bainbridge
Island and consequent pressure on groundwater resources; (3) concern about
landslide hazards; and (4) increased awareness of the role that the nearshore
zone plays in supporting marine resources.

Almost all post-glacial deposits, ice-contact deposits, most fault traces, and
most bedding traces were mapped from detailed lidar topography. Vashon till and
older strata were delineated on the basis of field observations, including
traverses and numerous dug or augured holes. Subsurface observations extracted
from a database compiled by GeoMapNW at the University of Washington
(http://geomapnw.ess.washington.edu) were used to refine the distribution of
till and older units.

[Summary provided by the USGS.]