Cheyenne River. The US uses about 600 million tons of coal a year, with about 40% of the coal coming from the Powder River Basin. The amount of coal coming from the Powder River Basin has been increasing over the last 20 years. The mines in the Powder River Basin typically have less than 20 years of life remaining. Almost all of the coal in the Powder River Basin is federally-owned, and further mine expansions will require a series of federal and state approvals, as well as large investments in additional mine equipment to begin the excavations. The majority of the coal mined in the Powder River Basin is part of the Fort Union Formation (Paleocene), with the low sulfur and ash content of the coal in the region making it very desirable. Coal supplies about a third of the United States' electricity supplies. The Powder River Basin mines supply approximately 40% of the coal that fuels those stations (mainly east of the Rocky Mountains) for generating electricity. The mines work in areas where the stripping ratio is between 1:1 (i.e. one ton of rock for one ton of coal) and 3:1. As the mines expand the stripping ratio will increase. As more rock must be moved (using large electrically powered draglines and diesel and electric mining trucks) the production cost will also increase. The mines are largely non-union operations with a history of squelching labor activity. According to historian Ryan Driskell Tate, surface mining in remote areas happened to reduce some of the "occupational togetherness" typically associated with coal miners working shoulder-to-shoulder underground in Appalachia. The environmental impact of mining on grass and aquifers has been a concern for surrounding ranchers who organized to resist new mines in the 1970s. Coal mining companies operating in the Powder River Basin Southern Powder River Basin Arch Coal (Black Thunder Mine, Coal Creek Mine) Black Hills Corporation/Wyodak Resources Development (Wyodak Mine) Contura Energy (Belle Ayr Mine, Eagle Butte Mine) Cloud Peak Energy (Antelope Mine, Cordero Rojo Mine) Kiewit Corporation (Buckskin Mine) Peabody Energy (North Antelope Rochelle Mine, Caballo Mine, Rawhide Mine) Western Fuels Association (Dry Fork Mine) Northern Powder River Basin Lighthouse Resources (Decker Mine) Cloud Peak Energy (Spring Creek) Westmoreland Coal Company (Absaloka Mine, Rosebud Mine) In June 2019, Peabody Energy and Arch Coal announced a joint venture for their combined Powder River Basin assets. Power plants fueled from Powder River