In 1999, 1,100 million short tons of coal were produced in the United States, 38 percent from the Northern Rocky Mountains and Great Plains region. This coal has low ash content, and sulfur content is in compliance with Clean Air Act standards (U.S. Statutes at Large, 1990).The National Coal Resource Assessment for this region includes geologic, stratigraphic, palynologic, and geochemical studies and resource calculations for 18 major coal zones in the Powder River, Williston, Green River, Hanna, and Carbon Basins. Calculated resources are 660,000 million short tons. Results of the study are available in U.S. Geological Survey Professional Paper 1625?A (Fort Union Coal Assess-ment Team, 1999) and Open-File Report 99-376 (Flores and others, 1999) in CD-ROM format.
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A summary of the U.S. Geological Survey 1999 resource assessment of selected coal zones in the Northern Rocky Mountains and Great Plains region, Wyoming, Montana, and North Dakota