Molly,
That is the Ft. Lupton Muzzle Loading Club.
The range abuts the restored Ft. Lupton in Colorado, a trading post originally built in 1840. just north of Denver. It strictly is for traditional muzzle loaders. There also is a "mountain man" style organization, The Tallow River Trappers associated with the South Platte Valley Historical Society at the location. Another active group that visits the site are the Buckhorn Skinners.
There are "Trappers Days" and Rendezvous activities throughout the year.
This is a picture of me attending the 1840 opening of the original trading post. I was much younger, then:
Ron