Coal resources of the San Juan Basin
— James E. Fassett

The coat resources of the San Juan Basin are concentrated in Upper Cretaceous rocks and were, for the most part, deposited in back-shore swamp environments developed in association with regressions of the Western Interior seaway's western shoreline. All of the thicker coal deposits are located southwest of thick, vertical buildups of adjacent (northeast) shoreface sandstones. Coals are low sulfur. high-ash, have heating values averaging from 9000 to 10,000 Btu (2300 to 2500 kg calories), and range from subbituminous to medium to low-volatile bituminous in rank. The Fruitland Formation contains more than 200 billion short tons of coal (93% of the basin total). Other important coal-bearing units are the Menefee Formation and the Gibson Coal Member and Dilco Coal Member (of the Crevasse Canyon Formation) These rocks may contain as much as 15 billion short tons of coal. San Juan Basin strip-coal mines produced 17.6 million tons of coal in 1987, down from a peak of 19.8 million tons in 1985. Nearly all of the basin's coal goes to feed electricity-generating power plants in New Mexico and Arizona. Over the past ten years Fruitland Formation coals have been found to contain large resources of coal-bed methane; recent studies estimate resources of 50 trillion cubic feet of gas. Commercial production of this gas is accelerating rapidly. mostly in the northern part of the basin.