This coverage contains the bedrock geology of the Linnton 7.5' quadrangle, Multnomah and Washington Counties, Oregon at 1:24,000-scale. The layer contains 11 separate map units representing volcanic and sedimentary rocks. This file is one in a set of four files which are provided to the user in two formats: MapInfo .tab and ESRI .shp format files. The other three files in the set include: Linnton_Bedrock, Linnton_Faults, and Linnton_Surficial. The quadrangle is located in the northwestern portion of the Portland urban area in NW Oregon. For the Linnton quadrangle, we have chosen to present two maps: a bedrock map that shows only the bedrock geology inferred to extend beneath the surficial deposits, and a companion map that shows only the surficial deposits.
The purpose of the project is to improve geologic mapping in the Portland urban area in order to better understand earthquake hazards. This coverage represent the most up-to-date, digital geology coverage currently available for the Linnton quadrangle.
The CD contains digital files with various map coverages created in MapInfo Professional version 9.1 (.tab) and a screen graphic of the map in Adobe PDF format. Digital map coverages are also provided as ArcView version 3.3 Shapefile (.shp) format for ESRI users. Accompanying the screen graphic of the map, is a text file (pdf format) describing the map units along with a discussion of the quadrangle's structural history. This digital data is not field-checked and comes with no guarantees as to its accuracy. Logs from Barber 1, an oil exploration well l in the map area, were interpreted and cutting samples from the well were geochemically analyzed (USGS, 2006) by Dr. Marvin Beeson and Mr. Terry Tolan. Data from this well was used in the preparation of the maps along with whole rock major and trace element geochemical analyses of approximately 74 samples of Columbia River Basalt and Boring volcanic field lavas. Several additional analyses were contributed by Dr. Ray Wells and Dr. Russ Evarts of the USGS.
Field work conducted in 2006 and 2007, data compilation-2008
DOGAMI makes no warranty as to the currency, completeness, accuracy or utility of any specific data. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that careful attention be paid to the contents of the metadata file associated with these data. User should use caution when overlaying other data sets and should not make legally binding decisions from this data. Any person using the information presented here should fully understand the data collection and compilation process before beginning their analysis/use. The burden of determining fitness for use lies with the user. To avoid the risk of misinterpretation, invalid results, and erroneous conclusions, the users must consider original map scale, collection methodology, and any other conditions specific to every data element and each dataset as a whole. Potential users are advised to consult with DOGMAI to gain an understanding of the inherent limitations of this data set and its scope of inference. Also, the user must be aware that errors and conditions originating from physical sources involved in developing a dataset may be reflected in the data, and that the digital processing performed during preparation, storage, and transmission of the dataset may have exacerbated such errors and/or introduced additional ones.
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This research was supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award number 03HQAG0013. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government. The Oregon Department of Geology and Mineral Industries created and maintains the spatial data sets. Credit should always be given to the data source and/or originator when the data is transferred or printed.
The geology was delineated by the geologist on a 1:24,000, 7.5-minute USGS topographic quadrangle, except for the Boring volcanic field. The Boring volcanic field was delineated using shaded relief images derived from LiDAR. Geologic contacts should be considered as approximate. Prior to release of map-on-demand files and metadata, the author was given final digital data sets and paper plots for checking against the source map(s) to verify the linework and attributes. Also, the author was asked to check the metadata and accompanying files for completeness and accuracy. Check plots of the map were reviewed by the mapper and cartographer for consistency with basic geologic principles and general conformity to USGS mapping standards. This data is not field-checked and is an interpretation of the mapper. No guarantees are provided as to its accuracy.
All polygons are closed and each polygon has one unique label; matching labels/polygons. In MapInfo Pro 9.1, the polygons were checked for polygon closure, erroneous or duplicate polygons, incorrect intersections, overshoots and undershoots (slivers and overlap), and node errors. Where found errors were corrected.
Spatial data is presented in the form of polygons characterizing the bedrock geology of the Linnton quadrangle. The bedrock geology maps from which the contacts, faults, and folds in these data sets were derived show the rock units that crop out at the surface or that are present beneath the soil or beneath relatively thin surficial deposits. The contacts of the soils themselves, or of surficial deposits such as alluvium and colluvium, are not included in the bedrock map.
Horizontal positional accuracy of this data with respect to the source map was verified by hard-copy plots.
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The geologic map was prepared using a variety of data sources, which were digitally integrated with MapInfo GIS software. The primary sources of data were field observations in natural and man-made exposures. Over 200 observations were recorded digitally in the field using a Fujitsu Pencentra tablet computer running ESRI Arcpad software. The field observations were located using a GPS unit linked to the Pencentratm, which allowed display of the GPS location on an DRG image of the 7½ minute topographic quadrangle map, allowing easy confirmation of the GPS position.
The second major source of data was the logs of over 1758 approximately-located water and engineering borings in the quadrangle. Borings were located by comparing owner, taxlot and address information on digital images of the logs (available online through the Oregon Water Resources Department) with ownership, address and taxlot information contained in the digital taxlot database for the area. Horizontal and vertical location errors were estimated for each located well and entered into the database. A limited number of wells were located in the field with GPS, for the remainder there was no field check performed.
Polygons geologic features and data points were hand digitized. The resultant coverages were attributed with data describing the geologic units, contacts, structures and point locations.
Draft check plots of the geologic map and explanation were created and submitted for peer review; description of Map Units and Correlation of Map Units finalized. Revisions were made to the geospatial database as needed. Prior to release of map-on-demand files and metadata, the author was given final digital data sets and paper plots for checking against the source map(s) to verify the linework and attributes. Also, the author was asked to check the metadata and accompanying files for completeness and accuracy.
Internal feature number.
ESRI
Feature geometry.
ESRI
Unit identification code
Oregon Department of Geology and Mineral Industries
This dataset has a polygon entity and attributes.
For a description of the structural geology, in addition to information relating to the data entities and attributes, please see the text that accompanies this publication.
The classification scheme for the field called "Unit" is a simple classification of single units, as follows:
Miocene-Pleistocene Volcanic and Fluvial Sedimentary Rocks
Boring volcanic field
QTbb = Basaltic andesite of Bonny Slope
Qbae = Basaltic andesite of Elk Point
Qbab = Bascalti andesite of Barnes Road
Qbk = Basalt of Kaiser Road
Th = Hillsboro Formation
Troutdale Formation
Ttg = Conglomerate and sandstone unit
Neogene Volcanic Rocks and Older Sedimentary Rocks
Columbia River Basalt Group
Wanapum Basalt
Frenchman Springs Member
Twfs = Basalt of Sand Hollow
Grande Ronde Basalt
Member of Sentinel Bluffs
Tgsb = Basalt of McCoy Canyon
Member of Winter Water
Tgww = Basalt of Winter Water
Member of Ortley
Tgo = Basalt of Ortley
Scappoose Formation
Ts = Marine sandstone unit
For complete decription of attributes, see O-08-06print.pdf
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Contact Nature of the Northwest Information Center by e-mail, phone, or letter explaining what products are needed. All DOGAMI publications, both in and out of print, are available for inspection at the Department's offices (most reports "on file" are in the Portland office only) and at many state-document depository libraries in Oregon, including most Oregon college and university libraries. Publications are also available via interlibrary loan from the Oregon State Library, State Library Building, Salem, OR 97310.
No warranty, expressed or implied is made regarding the accuracy or utility of the data described and/or contained herein, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that careful attention be paid to the contents of the metadata file associated with these data. The Oregon Department of Geology and Mineral Industries shall not be held liable for improper or incorrect use of these data. This information may be updated without notification.
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