CEMEX Niobrara Quarry

Lyons, Colorado

and photos by Ronald L. Parker, Senior Geologist, Borehole Image Specialists, P.O. Box 221724, Denver CO 80222 • ron@bhigeo.com

On a chilly day in late April, an intrepid group of RMAG members carpooled to Lyons, Colorado to venture on a rare, and soon-to-be impossible, field trip to the Dowe Flats Niobrara Quarry operated by CEMEX. The quarry is located on the N side of Highway 66, just to the E of Lyons, CO. Excavation at the quarry has ceased following denial of a 15-year permit extension by the Boulder County Commissioners on 9/29/2022. Currently, the quarry is under active reclamation, which is slated to be completed in 2 years. During reclamation, 2 million tons of the overburden stockpiled during quarry operation will be placed back into the open pits. The quarry is among the best exposures of the Niobrara along the Front Range, exposing the Codell up to the A Chalk. Because this exposure will be removed from view, the RMAG On-the-Rocks Field Trip was particularly compelling.

This OTR Field Trip was the in-person conclusion

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1: Alan Lindsey records the group excavating some very well-preserved bowl-shaped Inoceramids along bedding planes in the blocky Fort Hays at the NW corner of the quarry. View to the N. Alan is standing on the inclined top of the Codell. Note the inclined strata in the background.

2: The group is here taking in the East-dipping thrust fault in the middle of the outcrop. The feature appears on the N wall of the quarry.

3: Large, bowl-shaped Inoceramids on a bedding plane of the Fort Hays.