DOGAMI GEOLOGIC MAP SERIES
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GMS-130, Geologic map of the Milton-Freewater and Bowlus Hill 7.5′ Quadrangles, Umatilla County, Oregon, by Ian P. Madin, Jason D. McClaughry, and Carlie J.M. Azzopardi; 2 map plates (scale 1:24,000), plate of cross sections, and plate of explanatory text; Esri format geodatabase and metadata.
PUBLICATION DOWNLOADS
- Map plates (georefrenced PDFs), cross sections, explanatory text:
Plate 1, Geologic Map of the Milton-Freewater and Bowlus Hill 7.5′ Quadrangle, Umatilla County, Oregon (52" x 32"; 14.04 MB)
Plate 2, Bedrock Geologic Map of the Milton-Freewater and Bowlus Hill 7.5′ Quadrangle, Umatilla County, Oregon (52" x 32"; 12.70 MB)
Plate 3, Cross Sections to Accompany the Geologic Map of the Milton-Freewater and Bowlus Hill 7.5′ Quadrangles, Umatilla County, Oregon (52" x 42"; 1.72 MB)
Plate 4, Text to Accompany the Geologic Map of the Milton-Freewater and Bowlus Hill 7.5′ Quadrangles, Umatilla County, Oregon (52" x 42"; 15.39 MB)
- GIS data:
- Complete publication bundle (map plates, geodatabase, metadata; 48.40 MB zip file)
WHAT’S IN THIS PUBLICATION?
This publication provides an updated and spatially accurate geologic framework for the Milton-Freewater and Bowlus Hill 7.5′ quadrangles. Geologic data in the publication provide significant new details about the volcanic and structural geologic history of the area and the geologic conditions controlling the distribution of water resources, aggregate and other mineral resources, and geologic hazards.
INTRODUCTION [from Plate 4]
The Milton-Freewater and Bowlus Hill 7.5′ quadrangles in Umatilla County of northeast Oregon include an area of 270 square kilometers (km2) at the eastern edge of the Columbia Plateau, a broad depression forming the northwestern flank of the Blue Mountains (Figure 1). Milton-Freewater is the major population center in the map area, lying at the southern end of the Walla Walla Valley, overlapping the border of southeast Washington and northeast Oregon. The oldest rocks in the map area are part of the ~17 to 6 Ma (mega annum) Columbia River Basalt Group (CRBG), a succession of tholeiitic basalt and basaltic andesite lava flows cropping out over more than 210,000 km2 in parts of Washington, Oregon, Idaho, and Nevada (Figures 1 and 2; Plate 1; Reidel and others, 2013a). In the Milton-Freewater and Bowlus Hill 7.5′ quadrangles, the CRBG is locally overlain by upper Miocene and lower Pleistocene sedimentary rocks, lower Pleistocene to Holocene loess, Upper Pleistocene Missoula flood deposits, and Upper Pleistocene and Holocene alluvial units on valley floors (Plate 1). Three major fault zones converge in this part of the Columbia Plateau, including the WNW-striking Wallula fault zone, NNW-striking Milton-Freewater fault zone, and the NNE-striking Hite fault zone (Hooper and Conrey, 1989; Kuehn, 1995; Reidel and others, 2013b; Reidel and others, 2021; McClaughry and Azzopardi, 2023; Figures 1 and 3).
The geology and structure of the Milton-Freewater and Bowlus Hill 7.5′quadrangles was mapped by the Oregon Department of Geology and Mineral Industries (DOGAMI) between 2019 and 2021. Detailed geologic mapping in the Milton-Freewater and Bowlus Hill 7.5′quadrangles is a high priority of the Oregon Geologic Map Advisory Committee, supported in part by grants from the STATEMAP component of the U.S. Geological Survey (USGS) National Cooperative Geologic Mapping Program (NCGMP) under cooperative agreement G20AC00202 and by the Oregon Water Resources Department (OWRD) through Interagency Agreements DOGAMI/OWRD IAA #19 045. Additional funds were provided by the State of Oregon through DOGAMI.
The chief objective of this investigation is to provide an updated and spatially accurate geologic framework for the area as part of a multiyear study of the geology of the larger Walla Walla River basin. Additional key objectives of this project are to: 1) map individual CRBG flows and crosscutting faults to determine flow distribution, fault offsets, and fault history in this part of the Walla Walla River basin of northeast Oregon; and 2) characterize the stratigraphic framework and geologic conditions controlling the distribution of water resources within the CRBG. CRBG-hosted aquifers provide a critical water supply in the map area and more widely across the Pacific Northwest (Piersol and Sprenke, 2015). Earlier studies mapped the CRBG in highland areas bounding the Walla Walla Valley, but not below the extensive sedimentary cover that fills the valley to depths of 225 m (Swanson and others, 1981; Madin and Geitgey, 2007; Tolan and others, 2009). Textural and geochemical analysis of cuttings obtained from a number of water wells drilled in the Walla Walla Valley provide new information, essential to improve interpretations of the subsurface CRBG stratigraphy and structural geology of the region.
Primary map references consulted during this study include works by Hogenson (1964), Newcomb (1965), Walker (1973), Swanson and others (1981), Kuehn (1995), Hutter (1997), Derkey and others (2006), and Madin and Geitgey (2007). Soil information from Johnson and Makinson (1988) aided with mapping Quaternary surficial units. Additional references are cited in the Explanation of Map Units and in the DataSourcePolys feature class in the geodatabase.
The core publication products of this study are plottable geologic maps and cross sections (Plates 1, 2, and 3), an Esri ArcGIS™ geodatabase, and Microsoft Excel® spreadsheets tabulating point data for geochemistry, orientation points, and well data. The geodatabase presents new geologic mapping in a digital format consistent with the USGS NCGMP Map Schema (GeMS level 3; USGS NCGMP, 2020). It contains spatial information, including map unit polygons, contacts and faults, geologic lines, geochemistry points, orientation points, and well data, as well as data about each geologic unit such as age, lithology, mineralogy, and structure. Surficial and bedrock units in the geodatabase are depicted on Plates 1 and 2 at a scale of 1:24,000. Plate 1 includes a detailed geologic map showing both bedrock and surficial units, including concealed bedrock contacts. Plate 2 includes a simplified bedrock geologic map showing the distribution of contrasting bedrock lithologies and critical structural relationships. Plate 3 includes six geologic cross sections labeled A-A′ to F-F′. Plate 4 includes explanatory text, figures, and a data table.
GEOGRAPHIC INFORMATION SYSTEM (GIS) DATA
Geodatabase is Esri® version 10.7 format.
Metadata is embedded in the geodatabase and is also provided as separate .xml formatted files.
MAP PLATES (georeferenced PDFs)
Note: The map plate PDFs are in geospatial PDF format, allowing you to turn on and off layers in the map frame and to find geographic coordinates in the PDF.
Plate 1. Geologic Map of the Milton-Freewater and Bowlus Hill 7.5′ Quadrangle, Umatilla County, Oregon, scale 1:24,000, 52" x 32"
Plate 2. Bedrock Geologic Map of the Milton-Freewater and Bowlus Hill 7.5′ Quadrangle, Umatilla County, Oregon, scale 1:24,000, 52" x 32"
Plate 3. Cross Sections to Accompany the Geologic Map of the Milton-Freewater and Bowlus Hill 7.5′ Quadrangles, Umatilla County, Oregon, 52" x 42"
Plate 4. Text to Accompany the Geologic Map of the Milton-Freewater and Bowlus Hill 7.5′ Quadrangles, Umatilla County, Oregon, 52" x 42"