Western North Dakota contains an estimated 351 billion tons of lignite (brown coal), the single largest deposit of lignite known in the world. North Dakota also contains an estimated 25 billion tons of economically mineable coal, enough to last for over 800 years at the present rate of 32 million tons per year. The recorded history of lignite mining goes back to 1873 when small mines sprung up along the main routes of transportation in western North Dakota. At least 73 mines were operating in the state by 1900. Many of these were small, seasonal mines that removed coal from the face of the outcrop. They were called wagon mines because area farmers and ranchers would often bring their own wagons to the site to be filled with coal. Still, other mines were large operations employing hundreds of men with underground workings extending for thousands of feet.
By the early 1920s, there were approximately 250 mines operating in the state, with an equal number of underground and surface strip mines. The advent of the steam shovel increased the profitability of the surface mines and the last underground mine ceased operation in 1966. It is interesting to note that as early as the 1920s, geologists for the North Dakota Geological Survey were noting collapse features of underground mines and warning that these underground workings were going to be posing an increasing problem for the future.
Currently, there are six operations mining 32 million tons of coal annually in western North Dakota. Four operations (the Freedom Mine north of Beulah, the Knife River mine south of Beulah, the BNI mine at Center, and the Falkirk mine north of Washburn) are mining coal to feed steam boilers for electric generating plants in North Dakota. Two smaller operations (GeoResource's mine at Williston and the American Colloid mine at Haynes) are mining Leonardite (oxidized lignite) to be used in soil stabilization and as drilling fluid additives.