This photo covers that dark shadow that was the Rocky Mountain Arsenal:

Weapons manufactured at RMA included both conventional and chemical munitions, including white phosphorus (M34 grenade), napalm, mustard gas, lewisite, and chlorine gas.[6][7] RMA is also one of the few sites that had a stockpile of Sarin gas (aka nerve agent GB), an organophosphorus compound. The manufacture of these weapons continued until 1969. Rocket fuel to support Air Force operations was also manufactured and stored at RMA. Subsequently, through the 1970s until 1985, RMA was used as a demilitarization site to destroy munitions and chemically related items. Coinciding with these activities, from 1946 to 1982, the Army leased RMA facilities to private industries for the production of pesticides. One of the major lessees, Shell Oil Company, along with Julius Hyman and Company and Colorado Fuel and Iron, had manufacturing and processing capabilities on RMA between 1952 and 1982. The military reserved the right to oust these companies and restart chemical weapon production in the event of a national emergency.

They were also the source of man made earthquakes in the 1970’s when they were injecting waste liquid down a deep hole causing slippage underground!  As toxic dumps go this one is not at all bothersome as compared to the Rocky Flats Wildlife Preserve - a place that I’ve been once and won’t go back again.  They did a crap job of remediation AND buried 40 ft below the surface in the middle of the preserve is a room so toxic with Plutonium that when the plant was in operation NO ONE was allowed to go in that room after a certain point in it’s operation history - Takes 240,000 years to decay once - that’s some seriously frightening shit.

That being said I went to the Preserve today and found it amazing.  From where I live you have to go thru Commerce City which is one of the armpits of Colorado.  Refineries and other shit.  But once you’re there at the preserve all that melts away and it is absolutely glorious. I am a Bison Fanboy and love seeing these great beasts.

Downtown Denver