Thick Tertiary age coals make the Powder River basin of northeastern Wyoming the most prolific coal-bearing area in the United States, with an estimated remaining coal resource of more than 609 billion tons. The reserve base from the remaining resources is conservatively estimated at 45.6 billion tons. Whereas 23 billion tons of this reserve base is believed strippable, another 22.6 billion tons is probably recoverable by underground

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mining.

In 1977, coal production from seven strip mines amounted to 23 million tons or 50% of the state's total production that year. The Amax Coal Co. Belle Ayr mine alone accounted for 13.3 million tons. With expansion of the Belle Ayr mine to 17 million tons, the addition of three new mines, and the expansion of other existing mines, production in 1978 probably exceeded 39.2 million tons or about 63% of the state's 1978 production. Forecast annual production from the Powder River basin is 81.1 million tons by 1980 and 123.1 million tons by 1985. Of this tonnage, 95% is derived from the subbituminous Wyodak-Anderson coal bed, which ranges from 20 to 120 ft (6 to 36 m) thick in the east-central part of the basin.

In addition to conventional strip mining activity, two in-situ coal gasification projects are under way in the basin.

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