The graph on page 34. I read the section of the pdf on U.S. Reserves. The authors seem to be suggesting that U.S. coal production quality, on a btu basis, began going to hell in a hand basket in 1970, when the first western subbituminious and lignite began to be mined in measurable quantities.

EPA stiffened stack-gas emissions standards at this time, and the only coals that would pass were the western "clean" coals, an East West bituminous-subbituminous mix, or eastern bituminous of less than 1% sulphur content or abouts.

The decisions made were environmental and economic, and had nothing to do with a scarcity of eastern reseves.

The decisions allowed utilities to comply with EPA, without having to retrofit aging plants with realitively costly state-of-the-art emission controls.

Course my memory fails me often, at my advanced age.

The U.S. goverment currently believes that we possess 275 billion (estimated recoverable)Tons of coal or about 250 years' worth, at current rates of burn.

And what TechnoP said below too.

 

"When the abyss stares at me, it wets its pants." Brian Hopkins