Massive Slope Collapse Strikes Limestone Quarry

Around 3 p.m. on Jan. 18, 2023, a massive slope collapse struck the Rocky Mountain Industrials (RMI) limestone quarry. The collapse caused a rockslide about 300 feet wide. It brought boulders and huge slabs of limestone tumbling down onto the mined slope below.

A person in the vicinity described the noise as “multiple jet planes grumbling, getting closer and closer and getting louder and louder, for about 15 to 20 seconds.”

The debris spread across a large area of the quarry’s production bench and engulfed a front-end loader.

Luckily, quarry employees were all working elsewhere on the site that afternoon, and no injuries were reported.

Inspectors from the federal Mine Safety and Health Administration and the Colorado Division of Reclamation, Mining and Safety visited the quarry and studied the slope collapse in the ensuing days.

Bobby Wagner, RMI vice president of engineering, told state inspectors that the slide first broke loose on the west side of the quarry, where the limestone deposit tilts downward at a 45-degree angle.

A highwall on the east side of the quarry, where the limestone tilts downward at a less-steep, 30-degree angle, did not break loose. RMI blasted in this area most recently on Dec. 13, 2022.

The area that broke loose had not been mined since before RMI purchased the quarry operation in 2016, but RMI was actively mining limestone below the slide area.

Both agencies issued notices of enforcement actions for suspected permit violations.


This page will be updated as these enforcement actions move forward.

The slope collapse at the Rocky Mountain Industrials limestone quarry occurred around 3:00 p.m. on Jan. 18, 2023. This image was captured shortly after the collapse occurred, as dusk moved across the landscape.

An overhanging cliff face remains at the top of the collapsed slope at the Rocky Mountain Industrials limestone quarry.

Permit Enforcement Actions by Federal and State Agencies

U.S. Mine Safety and Health Administration (MSHA)
Control 103(k) Order No. 9154256

Issued Jan. 19, 2023, at 5:00 p.m. by Matthew Lemons, District Manager for Colorado, MSHA

Description of incident:
“A non-injury accident occurred at this mine on 1/18/2023 when the highwall of the limestone quarry collapsed at about 1500 hours. The huge landslide from the top of the highwall covered the benches below and overwhelmed the catch basin on the mine floor and partially covered an unoccupied Cat 966 front-end loader.”

103(k) Order:
“No miner will be permitted in the quarry except by MSHA authorization while this order is in place. This order, which includes all of the quarry and the crusher plant located on the quarry floor, is issued to assure the safety of all persons in the mine and will remain in place until it is safe to resume normal mining operations in the quarry.”

The order applies to:
“All of the quarry including the face, the highwall, the quarry floor where the crusher plant is located, and the road leading into the quarry floor.”

Requirements for Rocky Mountain Industrials:
“The operator will provide MSHA a written plan to recover the Cat 966 loader and a written plan to recover the benches and face stability in the quarry.”

Download the MSHA 103(k) of Jan. 19, 2023 (obtained from MSHA by GSCA via a Freedom of Information Act request)

Colorado Division of Reclamation, Mining and Safety (DRMS)
Reason to Believe a Violation Exists

Issued Jan. 25, 2023, by Virginia Brannon, DRMS Director

Colorado DRMS mine inspectors Amy Yeldell and Dustin Czapla visited the quarry on Jan. 23. Bobby Wagner, RMI vice president of engineering, and Brian Fallin, RMI CEO, accompanied the state inspectors.

Yeldell produced a detailed report describing the slide, including photos of the debris in relation to quarry facilities and highwalls. (Document links below.)

On Jan. 25, DRMS Director Virginia Brannon issued a letter to RMI citing a possible violation of the company’s state mining permit and calling RMI to appear before the Colorado Mined Land Reclamation Board for a formal public hearing.

The Jan. 25 letter set a hearing date for the board’s March 22-23 meeting. In mid-February, DRMS agreed to postpone the hearing to the board’s April 19 meeting. Deep snow cover and wintry weather were limiting access to the area.

Prior to the April 19 hearing, DRMS staff and RMI reached a Stipulated Agreement. It was approved at the April 19 MLRB meeting.

Conditions of the Stipulated Agreement are:

  • RMI acknowledges “awareness” of its failure to protect areas outside its permit boundary from slides or damage.
  • A cease-and-desist order is imposed on the production bench until a technical revision to RMI’s mining permit is approved by DRMS.
  • RMI must seek a technical revision to its permit to establish a long-term geologic monitoring and stability plan. The application must include a geotechnical stability plan prepared by an accredited engineering firm.
  • RMI must coordinate its efforts with MSHA and BLM to ensure that monitoring and stability analysis and plans meet their requirements.
  • Any disturbance to lands outside RMI’s state mining permit boundary will require a permit amendment.
  • Failure to comply may lead to an enforcement hearing before the MLRB.

Watch the hearing on the DRMS YouTube channel. (Fast-forward to 0:40:00 to view the RMI agenda item.)

Archive of DRMS documents

DRMS 01-25-2023 Notice of Possible Violation, Inspection Report with photos (11 pages, 14.4 MB)

DRMS 01-25-2023 Notice of Possible Violation cover letter (2 pages, 2 MB)

DRMS 01-25-2023 Inspection Report without photos (3 pages, 5.4 MB)

DRMS 01-25-2023 Inspection Report with photos (9 pages, 12.3 MB)

DRMS 04-19-2023 Stipulated Agreement (4 pages, 338 KB)