Aggregate Resources
Sand, gravel, and bedrock may be mined or quarried to produce raw materials known as 'construction' aggregate. Construction aggregate is used for road base and stabilization as well as in the manufacture of concrete, asphalt, and other products. These products are the building blocks for our homes, businesses, roads, and bridges.
In 2024, the United States produced about 38 billion dollars worth of sand, gravel, and crushed stone aggregate, with production in Washington worth about 780 million dollars, or about two percent of the national total (Mineral Industry Surveys). Aggregate is currently the most valuable mineral commodity produced in Washington. To learn more about how aggregate is commonly mined, check out the "Common Aggregate Mining Practices" section below.
Identifying and protecting sources of aggregate are critical for economic growth, resource management, and maintaining the quality of life enjoyed by those who live in Washington. WGS is mapping aggregate resources in Washington on a county-by-county basis. County and city planners can use aggregate resource maps to assist their decision-making in long-term land-use planning. See the interactive map in the Available Maps, Ongoing Projects, and Future Projects section below to view the areas that have already been mapped or are scheduled to be mapped. To learn more about this mapping effort, check out our Aggregate Resource Mapping in Washington fact sheet.
With proper planning and reclamation, former mined areas can be reclaimed as habitat for wildlife, converted into city parks, or adapted for other uses. The Surface Mine Reclamation Program monitors surface mines, issues reclamation permits, monitors site reclamation compliance, and provides consistent regulation of mining sites statewide. To learn more about WGS’s Surface Mine Reclamation Program, visit their webpage.
- Aggregate Resources and the Growth Management Act
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Planning for future aggregate usage is required under the Revised Code of Washington (RCW) 36.70A.131 and the Washington Administrative Code (WAC) 365-190-070. Counties and cities must identify and designate Mineral Resource Lands of long-term commercial significance. Mineral Resource Lands include aggregate resources.
Aggregate production in Washington State is generally increasing, with fluctuations due to economic conditions. The chart below shows annual aggregate production from 1971 to 2023 (National Minerals Information Center), plotting construction sand and gravel (blue) and crushed stone (orange) separately. In Washington, production of construction sand and gravel is higher than that of crushed stone due to the abundance of sand and gravel deposits. Production of both aggregate commodities were impacted by the 2008 recession when construction and development decreased nationally. Current production levels have not fully recovered to pre-recession highs.
Annual aggregate production in Washington State from 1971 to 2023. Data source: USGS Aggregates Time Series Data by State, Type, and End Use. The Growth Management Act (GMA) states that counties and cities should use information provided by the Department of Natural Resources (DNR), the U.S. Geological Survey, and any other relevant information provided by property owners for their land-use decisions related to mineral resources and Mineral Resource Lands (MRLs). MRLs are a land-use designation and each local jurisdiction determines their MRLs. In general, MRLs are where mineral resources could be mined or quarried with the proper permits. Rarely, some jurisdictions will allow permitted mining activities in lands not designated as MRLs.
Aggregate resources, which are a part of mineral resources, are being mapped by the Washington Geological Survey (WGS). Cities and counties may choose to use all or part of the information provided by WGS when they determine which mineral resources to designate as MRLs.
To learn more about how WGS is involved with GMA, visit WGS's Geologic Planning webpage.
- How Aggregate Resource Maps Are Made
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Aggregate resources are commonly thought of as ubiquitous, meaning that they can be found everywhere. However, aggregate resources are deposited in specific geologic areas and their quality can vary significantly. In general, glacial deposits, river deposits, and some types of igneous rocks have been most commonly mined for aggregate resources in Washington. WGS’s aggregate resource maps highlight areas that could have suitable aggregate resources according to our quality and quantity thresholds. The maps also communicate areas where unsuitable aggregate resources are likely to be found. Unsuitable areas could include resources that are of poor quality or are either not large enough or thick enough to be mined. Federally protected lands such as National Parks or Wilderness areas are not analyzed for this project because they have restrictions that do not allow new mining to occur.
Diagram showing data that go into WGS aggregate mapping (left) and an example of a resulting aggregate resource map (right). Aggregate resource maps are made using existing geologic maps, subsurface data, materials-testing data, and publicly available mining data to classify potential sources of aggregate. These classifications vary based on size, quality, and uncertainty of the resource. We show sand and gravel resources separately from bedrock resources because there are differences in their source geology and in how they are mined.
In general, aggregate resources are classified as either Demonstrated, Inferred, or Speculative resources. Areas where aggregate resources are unlikely found are classified as Not a Resource. Maps published prior to 2023 use different resource classification language. To understand more about the resource classifications in the map area you are interested in, refer to the resource classification descriptions outlined in the publication’s pamphlet.
Diagram showing classification scheme for WGS aggregate mapping. - Available Maps, Ongoing Projects, and Future Projects
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Click on the map below to download completed (green) aggregate resources maps, and view our in progress (orange) and scheduled (red) aggregate resource mapping areas.
Click here to open the map in full screen.
- How Can Planners Use the Aggregate Resource Maps?
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City and county planners can use WGS’s aggregate resource maps and corresponding data to make more informed decisions about designating and revising Mineral Resource Lands (MRL) in their jurisdictions. While aggregate resource maps show where there is evidence for aggregate resources, they do not factor in current land use or other considerations. Overlaying aggregate resource data with the county and city zoning, transportation, environmental, site-specific information, and other data will help each jurisdiction make county- and city-specific decisions.
According to RCW 36.70A.131, counties and cities shall take into consideration new data available from the Department of Natural Resources as part of the review required by RCW 36.70A.130. WGS will reach out to relevant counties and cities before and during the mapping process. Once the map and data are published, these jurisdictions are able to use these new data for land-use and other decision-making tasks. To learn more about land-use, visit the Department of Commerce's Growth Management Services webpage.
- Common Aggregate Mining Practices
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Sand and gravel mining commonly occurs in large open pits. Typically, sand and gravel are relatively dry and removed with bulldozers, front-end loaders, and other conventional construction equipment. However, mining may occur in areas with a high water table. In this case, sands and gravels are removed by a mining method known as dredging. Dredge mining requires specialized equipment such as draglines or clamshell excavators.
Bucket dredge in gravel pit operated by Miles Sand & Gravel, Inc., near Roy, WA. Photo by Carrie Gillum (DNR). Crushed rock mining differs from sand and gravel in that it must be drilled and blasted to be removed. Blasting requires loading a small amount of explosives into regularly drilled holes in the rock face. When detonated, the explosives fracture the rock in mere seconds. This breaks the rock into smaller pieces suitable for crushing.
Crushed rock piles in Skagit County, WA. Photo by Eli Newby (DNR) After extraction, the sand and gravel or crushed rock is sorted into piles of various sizes. It may vary from boulder to sand sized. The size of the rock needed may depend on construction project requirements and many sizes of aggregate may be required.
Once purchased, aggregate is transported to the construction site by trucks, railcars, or barges. Of these transportation methods, 93% of all aggregate is shipped by trucks nationally. These vehicles vary in size from pickups to 28-ton haulers. Because several gravel pits around Puget Sound transport aggregate by barge, Washington State would differ slightly from the national values shown.
- Fun Facts!
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- In November 2021, the Federal Infrastructure Investment and Jobs Act was signed into law. The legislation includes investing $110 billion nationwide to repair roads and bridges. These projects will increase the need for construction aggregate nationwide through 2026.
- Washington State produced 54.8 million U.S. tons of aggregate worth $686 million dollars in 2023, enough material to fill 13,000 Olympic-sized swimming pools.
- Washington is the sixth-largest producer of sand and gravel resources in the country (Mineral Industry Surveys).
- Washington has ~875 active permitted aggregate mines (WGS Active Surface Mine Permit GIS data).
- A 25-mile haul will double the cost of most aggregate related products (Pacific Lutheran University School of Business, 2003).
