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Riley Pass Uranium Mine

Site Background and History

The Riley Pass Uranium Mine Project is located within the North Cave Hills area of the Sioux Ranger
District, Custer Gallatin National Forest (CGNF), Harding County, South Dakota. The nearest town is
Ludlow, South Dakota which is 5 miles east of the project site. Elevations range between 3,100 to 3,400
feet above mean sea level. A small area of the Riley Pass Uranium Mine project site is located on private
land. The project site consists of 12 bluffs: Bluff A, Bluff B, Bluff C, Bluff D, Bluff E (later combined into
one area called ‘Bluff CDE’), Bluff F, Bluff G, Bluff H, Bluff I, Bluff J, Bluff K, and Bluff L for approximately
300 impacted acres. Each bluff includes a disturbed area requiring reclamation of a range between 6
acres to 153 acres.

A map titled Riley Pass Uranium Mines Site Regional Map. In the top Left corner of the map is an image of the state of Montana with a dot in the northwest corner of the state indicating this map's location. Locations identified on the map inclued: Ducks Unlimited Pond, Brown's Pond, Schleichart Draw Reservoir, Bluff A, Bluff B, Bluff CDE, Bluff F, Bluff G, Bluff H, Bluff I, Bluff J, Bluff K.Bluff ABluff BBluff CDEBluff FBluff GBluff HBluff IBluff JBluff KBluff L

Recreation

The North Cave Hills land unit is a popular destination for recreationists of all kinds. The cliff edged
mesas of ponderosa pine and green ash draws offer unique and beautiful scenery. While spring and fall
hunting seasons are often the busiest; the North Cave Hills sees bicyclists, horseback riders, hikers,
campers, star gazers, and bird watchers throughout the year. Off Highway Vehicles such as dirt bikes
and 4-wheelers are common sights. Many people also come to the North Cave Hills to fill firewood
permits and Christmas tree tags.

Cultural Significance

The North Cave Hills is a historically significant area of South Dakota that was heavily utilized
prehistorically by many Plains tribes, and historically as early as 1864 by explorers, fur trappers, and
later homesteaders and ranchers. The CGNF is currently working with tribal governments and other
interested parties to develop methods to preserve or protect the prehistoric and historic resources that
may be affected by the Riley Pass reclamation project, as well as resources throughout the North Cave
Hills.

Mining History

In 1954, uranium exploration in the North Cave Hills began. Between the mid-1950s and early 1960s,
strip mining occurred in the area. By 1964, all mining in the area ceased. Mining activities included
pushing the overburden off the bluff top and onto the steep sides of the bluffs below the rim rock to
uncover the uranium-bearing lignite coal beds. These coal beds were removed for uranium processing
off-site. Mining resulted in piles of mine spoils with heavy metal and radioactive contamination and lack
of vegetation to anchor it in place which contributes to transport of contaminated sediments from
surface water runoff and wind. Mining in the area occurred prior to today’s requirements for
environmental restoration resulting in the degraded and unstable landscape found today. An estimated
300 acres are impacted by disturbed bluffs, overburden piles (spoils), hazardous erosional features,
highwalls, elevated radioactive materials, and heavy metals.

Reclamation

Reclamation is being performed in accordance with the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA; 42 USC Chapter 103). The USFS is the lead agency over the
reclamation activities as the Riley Pass Uranium Mine Project site is primarily on National Forest System
(NFS) lands and the source of the release or potential release of hazardous substances is from NFS lands.
In 1996, Kerr-McGee (predecessor to Tronox) was notified of potential liability for hazardous materials
at the Riley Pass Uranium Mine project site. In 2009, Tronox filed for bankruptcy and an initial
settlement was reached for an initial payment of funds for cleanup of the site. A second settlement
agreement was finalized in 2014 between Anadarko (who acquired Kerr-McGee) and the US to fund
cleanup on thousands of contaminated sites which were once operated by Kerr-McGee. Riley Pass is one
of these sites.

The basis for the reclamation plan is provided in the 2006 Final Engineering Evaluation/Cost Analysis (EE/CA) and the most recent, 2016 Action Memorandum. Additional information can be found on the Previous Action Memorandums. A release or a significant threat of release has or is occurring at the Site that poses a threat to public health or welfare or the environment, on and/or from lands under the NFS Lands. Conditions at the Site present an imminent and substantial endangerment to human health and the environment due to the high concentrations of arsenic, molybdenum, thorium, uranium, and radium-226 (Ra-226) metals and radionuclides found in the soils and sediment from the mining area. Based on studies performed at the Site, if cleanup criteria for arsenic (142 milligrams per kilogram) and Ra-226 (30.0 picoCuries per gram) were met, all other contaminants of potential concern would be reclaimed along with these two contaminants.

 

Current Reclamation Status

Bluff

Status (date)

Acreage

Percent of Total (%)

A

Reclaimed (2020)

6

2%

CDE

Reclaimed (2017)

33

11%

F

Reclaimed (2016)

8

3%

G

Reclaimed (2016)

7

2%

I

Reclaimed (2016)

26

9%

K(2)

Reclaimed (2016)

5

2%

J

Reclaimed (2017)

9

3%

K

Reclaimed (2010)

11

4%

B

Unreclaimed

153

51%

H

Unreclaimed

34

11%

L

Unreclaimed

10

3%

Natural Landform Design

Reclamation at Riley Pass is utilizing a new technique that is based on replicating features of the surrounding natural landscape. This landform inspired design approach emphasizes diverse surface topography, multiple slope angles and aspect, small drainage basins, natural stream morphology, and differing vegetation patterns.  The pre-mine landscape represents what the area had evolved to and by incorporating similar features, the aim is to jump start natural geomorphological processes and restore disturbed areas to a stable and visually unified landscape. The ultimate goal of this natural landform design approach is to minimize site maintenance and ensure reclaimed slopes blend into the native landscape to be stable as well as indistinguishable from undisturbed areas.

Image
A photo of a land area with two plateaus with exposed soil across the top of the plateaus. Two dirt roads run between the two plateaus.

Photo showing the complex drainage channels on the reclaimed slopes. Reclaimed area at Riley Pass, 2016, Riley Pass, Sioux District of Custer Gallatin National Forest.
View full-sized photo on Flickr
 

(USDA Forest Service photo.)
Image
A photo of a land area that has dried golden colored grass and ridges with rock outcrops.

Undisturbed area at Riley Pass, 10/18/2022, Riley Pass, Sioux District of Custer Gallatin National Forest. View full-sized photo on Flickr

(USDA Forest Service photo by Annica Brown.)
Image
A photo of a land area with white text above two plateaus that states: Undisturberd bluff above the plateau on the left and Reclaimed bluff above the plateau on the right.

Photo –Undisturbed Bluff vs. Reclaimed Bluff at Riley Pass, 6/2/2021, Riley Pass, Sioux District of Custer Gallatin National Forest. View full-sized photo on Flickr.

( USDA Forest Service photo by Dakota Drone Works (Luke Lundberg).)

Last updated August 27th, 2025

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