We are excited to announce the publication of the Aggregate Resource Inventory of Skagit County. The full report is now available for download [ZIP (26.5 MB)].
What are aggregate resources?
Sand, gravel, and bedrock may be mined or quarried to produce raw materials known as construction aggregate. Construction aggregate is used in the manufacturing of concrete, asphalt, and other essential materials for roads, homes, businesses, and bridges.
Why are we mapping aggregate resources?
By law, counties and cities are required to identify and designate aggregate of long-term commercial significance. To support cities and counties in this mission, the Washington Geological Survey (WGS) is publishing county-scale aggregate resource maps. These publications are designed to be a helpful tool for planners, and provide a better understanding of Washington’s nonrenewable sand, gravel, and bedrock resources. These publications will also benefit engineers, transportation departments, and industry by identifying areas where geologic conditions suggest the presence of potential aggregate sources.
Aggregate resource mapping projects goals
Publish aggregate resource inventories for each county with the eventual goal of full Washington State coverage.
Provide our data in formats that are accessible to a broad audience, including GIS users. To meet this goal, the multi-county aggregate resources database is available on the interactive Geologic Information Portal, and as a zip-file download package with accompanying metadata on our Geology GIS Data and Databases webpage.
Increase awareness and understanding of this project by working closely with interested parties early in the project and providing regular updates as we complete our work.
Offer continued data support and outreach after each county-scale project has been completed.
What’s next for our aggregate resource mapping effort?
Next, we will map aggregate resources in Spokane County. Initial project outreach for Spokane County was completed last fall, and project work started in January. The publication timeline for this work is still being finalized.
Contact us if you have any questions about the Skagit County publication, or our future mapping plans:
Amy Rudko, Aggregate Mapper
Email: amy.rudko@dnr.wa.gov
Work cell: (360) 764-6340
Tricia Sears, Geologic Planning Liaison
Email: tricia.sears@dnr.wa.gov
Work cell: (360) 628-2867
Links
The map plate and accompanying pamphlet for Skagit County aggregate resources are available as a zip file containing two PDFs.
More information is available on the Washington Geological Survey Aggregate Resources web page.
Click here to view a PDF factsheet on the aggregate resources project.
To learn more about integrating aggregate resources, geologic hazards, and climate resilience into land-use planning, check out the Washington Geological Survey Geologic Planning web page.
The geospatial data used to develop the map sheet are available as a zip-file download package with accompanying metadata on our Geology GIS Data and Databases website. An interactive web-based version of the Aggregate Resources Database is also available on the WGS Geologic Information Portal.
Abstract from publication
This aggregate resource inventory for Skagit County identifies potential sources of aggregate—both sand and gravel, and bedrock (rock and stone)—using a combination of surficial and bedrock geologic mapping, subsurface information from boreholes and water wells, aggregate testing data, and records of current and historical mining activity. The aggregate resource classification scheme assesses both the quality and quantity of potential resources, and communicates that assessment using four classifications: Demonstrated, Inferred, Speculative, and Not a Resource. Areas that overlap with North Cascades National Park, Ross Lake National Recreation Area, federal wilderness areas, and National Wild River segment designations were not analyzed for this study. In total, our inventory classifies 319,431 acres of land as having the potential for economically significant aggregate resources, which is about 29 percent of the county’s land area. For sand and gravel resources mapped as Demonstrated and Inferred (our highest-certainty resource classifications), we estimate 1.3 to 2.9 billion cubic yards of aggregate (2.1 to 5.3 billion tons). Due to the difficulty of quantifying the thickness of bedrock aggregate resources, we did not estimate their volume or tonnage.
Approximately 17,716 acres (6%) of areas we identify as potential sources of aggregate may be inaccessible for resource extraction because they are on land classified as developed according to the National Land Cover Database. A service-area analysis reveals a possible high stress on the limited number of active aggregate mines in the central and eastern portion of the county to serving the aggregate needs of maintaining Highways 20 and 530. An additional analysis explores opportunities to minimize transportation costs by prioritizing future sources of aggregate nearest to areas of aggregate demand. This assessment uses a road-network transportation analysis that identifies 41 percent of the aggregate resource areas in our inventory as being within a 20-mile driving distance from a variety of points of aggregate demand.
Suggested citation
Rudko, Amy; Steely, A. N., 2024, Aggregate resource inventory of Skagit County, Washington: Washington Geological Survey Map Series 2024-01, 1 sheet, scale 1:100,000, with 21 p. text. [https://www.dnr.wa.gov/publications/ger_ms2024-01_agg_map_skagit_100k.zip]
WASHINGTON STATE GEOLOGY NEWS 