The work from which this material is drawn has been conducted with the support of the New Mexico Research and Development Institute and six coal companies. However, the authors remain solely responsible for the content of this publication.

During three years of drilling and sampling in the San Juan Basin, 522 coal core samples were collected from 149 drill sites, located on approximate 2 mi centers in the Fruitland, Menefee, Crevasse Canyon, and Moreno Hill Formations. Most of these drill sites were placed along the lines parallel to the Cretaceous shorelines in areas where thickest coals are at depths of about 250 ft, i. e. potentially strippable. Eight drill sites in the Chacra Mesa field were drilled on a line perpendicular to the shorelines on 1 mi centers; the Moreno Hill Formation sites in the Salt Lake field and the Fruitland Formation in the Fruitland field were drilled on trends perpendicular to the Late Cretaceous shorelines.

Coals analyzed from the Fruitland Formation were from the Fruitland, Bisti, and Star Lake fields; those analyzed from the upper member of the Menefee Formation were from the Chacra Mesa and La Ventana fields; those from the Cleary Coal Member of the Menefee Formation were from La Ventana, Chacra Mesa, San Mateo, and Standing Rock fields; and the remaining Menefee coals analyzed were from the Monero field. Cleary-Gibson, Gibson, and Dilco Coal Member coals of the Crevasse Canyon Formation were cored and analyzed from the Gallup and Crownpoint fields, and coals from the Moreno Hill Formation were collected and analyzed from the Salt Lake field.

Significant aspects of chemical, quality, coal rank, thickness trends, stratigraphic-depositional features, and petrographic composition are presented in this report. Petrographic analyses indicate a difference in maceral content between the Fruitland coals and the other older formations sampled. The Fruitland coals have a higher percentage of liptinite, in particular the resinite constituent of the liptinite group is much higher than for the Menefee and Crevasse Canyon coals. In general, the Fruitland coals have a higher hydrogen/volatile matter ratio which is influenced in part by the resinite content. The Moreno Hill Formation coals in the Salt Lake field have the highest inertinite content of the all the formations sampled, indicative of oxidation during coal development.

The Fruitland coals tend to be the most economically viable because of their thickness, relative continuity, and overall quality, albeit having a high ash content. The Menefee Formation coals do not have the same degree of bed continuity or thickness as the Fruitland coals, but the ash content is lower and the rank is equivalent to that of the Fruitland coals in the Bisti and Star Lake fields. The Menefee Formation coals, with the exception of those in the San Mateo field, have a relatively high sulfur (>1%) content. Of the Menefee Formation coal fields investigated, the San Mateo field has the best economic potential because of the thickness of the coals and the low sulfur and ash content. The Cleary-Gibson coals in the Gallup area have the greatest economic potential of the Crevasse Canyon fields examined. This coal-bearing sequence has both multiple coal beds and relatively thick coals. The Cleary-Gibson coals also have low ash and sulfur contents which enhance their economic potential.

Of the remaining fields drilled, the upper member Menefee coals in the La Ventana field and the Crevasse Canyon coals in parts of the Crownpoint field may have economic potential. The La Ventana upper member coals are relatively thick and have a low ash content. In the Crownpoint field, the coals are thickest in the area northwest of the town of Crownpoint and near Borrego Pass.