Geologic map and database of the Salem East and Turner 7.5 minute quandrangles, Marion County, Oregon: A digital database, USGS OFR 00-351

This database and accompanying plot files depict the distribution of geologic
materials and structures at a regional (1:24,000) scale. The report is
intended to provide geologic information for the regional study of materials
properties, earthquake shaking, landslide potential, mineral hazards, seismic
velocity, and earthquake faults. In addition, the report contains new
information and interpretations about the regional geologic history and
framework. However, the regional scale of this report does not provide
sufficient detail for site development purposes. In addition, this map does
not take the place of fault-rupture hazard zones designated by the Oregon State
Geologist. Similarly, the database cannot be used to identify or delineate
landslides in the region.

This digital map database, compiled from previously published and unpublished
data, and new mapping by the authors, represents the general distribution of
bedrock and surficial deposits of the Salem East and Turner 7.5 minute
quadrangles. A previously published adjacent geologic map and database by
Tolan, Beeson, and Wheeler (1999) contains a text file (geol.txt or geol.ps),
it provides current information on the geologic structure and stratigraphy of
the area covered. The database delineates map units that are identified by
general age and lithology following the stratigraphic nomenclature of the U.S.
Geological Survey. The scale of the source maps limits the spatial resolution
(scale) of the database to 1:24,000 or smaller.

The Salem East and Turner 7.5-minute quadrangles are situated in the center of
the Willamette Valley near the western margin of the Columbia River Basalt
Group (CRBG) distribution. The terrain within the area is of low to moderate
relief, ranging from about 150 to almost 1,100-ft elevation. Mill Creek flows
northward from the Stayton basin (Turner quadrangle) to the northern Willamette
Valley (Salem East quadrangle) through a low that dissects the Columbia River
basalt that forms the Salem Hills on the west and the Waldo Hills to the east.
Approximately eight flows of CRBG form a thickness of up to 700 in these two
quadrangles. The Ginkgo intracanyon flow that extends from east to west through
the south half of the Turner quadrangle is exposed in the hills along the
southeast part of the quadrangle.

The major emphasis of this study was to identify and map CRBG units within the
Salem East and Turner Quadrangles and to utilize this detailed CRBG
stratigraphy to identify and characterize structural features. Water well logs
were used to provide better subsurface stratigraphic control. Three other
quadrangles (Scotts Mills, Silverton, and Stayton NE) in the Willamette Valley
have been mapped in this way (Tolan and Beeson, 1999).

The databases in this report were compiled in ARC/INFO, a commercial Geographic
Information System (Environmental Systems Research Institute, Redlands,
California), with version 3.0 of the menu interface ALACARTE (Fitzgibbon and
Wentworth, 1991, Fitzgibbon, 1991, Wentworth and Fitzgibbon, 1991). The files
are in either GRID (ARC/ INFO raster data) format or COVERAGE (ARC/INFO vector
data) format. Coverages are stored in uncompressed ARC export format (ARC/INFO
version 7.x). ARC/INFO export files (files with the .e00 extension) can be
converted into ARC/INFO coverages in ARC/INFO (see below) and can be read by
some other Geographic Information Systems, such as MapInfo via ArcLink and
ESRI's ArcView (version 1.0 for Windows 3.1 to 3.11 is available for free from
ESRI's web site: "http://www.esri.com"). The digital compilation was done in
version 7.1.1 of ARC/INFO with version 3.0 of the menu interface ALACARTE
(Fitzgibbon and Wentworth, 1991, Fitzgibbon, 1991, Wentworth and Fitzgibbon,
1991). The geologic map information was digitized from stable originals of the
geologic maps at 1:24,000 scale. The author manuscripts (pen on mylar and pen
on paper) were scanned using a Anatek rasterizing color scanner with a
resolution of 600 and 400 dots per inch. The scanned images were vectorized
and transformed from scanner coordinates to projection coordinates with digital
tics placed by hand at quadrangle corners. The scanned lines were edited
interactively by hand using ALACARTE, color boundaries were tagged as
appropriate, and scanning artifacts visible at 1:24,000 were removed.