From today’s edition of the Energy Information Administration’s Energy Today site:

Coal production from mines with mountaintop removal (MTR) permits has declined since 2008, more than the downward trend in total U.S. coal production. Total U.S. coal production decreased about 15% from 2008 to 2014. Surface production decreased about 21%, and mountaintop removal, one type of surface production, decreased 62% over this period. Lower demand for U.S. coal, primarily used to generate electric power, driven by competitive natural gas prices, increasing use of renewable generation, flat electricity demand, and environmental regulations, has contributed to lower U.S. coal production.

Worth noting, though, is this disclaimer:

By identifying the mines that have MTR permits, it is possible to estimate MTR production using mine production data. However, quantifying the amount of coal produced from mountaintop mining is difficult, because there are a variety of mining techniques that can be performed on a mountaintop in addition to mountaintop removal. These techniques include contour mining, where coal is mined on a hillside, and area mining, where coal is mined from relatively flat terrain. Some of these non-MTR methods may be used in conjunction with or following the use of MTR, making attribution of coal production by mining method less obvious. Consequently, production data in this article refer to total surface production at mines with MTR permits and provide an upper bound of MTR production.