Geologic assessment of coal in the Colorado Plateau : Arizona, Colorado, New Mexico, and Utah / edited by M.A. Kirschbaum, L.N.R. Roberts, and L.R.H. Biewick. - Kirschbaum, Mark A.; Roberts, Laura N. Robinson.; Biewick, Laura H. (U.S. Dept. of the Interior, U.S. Geological Survey, 2000)