“…Economically important coal zones are present in many of the regressive marine cycles, and some coal and carbonaceous shale are present throughout the fluvial part of the Mesaverde as well. Coal rank maps based on vitrinite reflectance have been generated for coal zones associated with marine regressive cycles (Freeman, 1979;Johnson, 1983, 1986), and many vitrinite reflectance profiles through the Mesaverde are available (Bostick and Freeman, 1984; Chancellor and Johnson, , 1988Johnson and Nuccio, 1986;Nuccio and Johnson, 1989a). The position of several key vitrinite reflectance levels has also been generally determined in the Piceance basin (Johnson and others, 1987).…”