Coal resources of Upper Cretaceous Fruitland Formation in the Southern Ute Indian Reservation, southwestern Colorado

Coal resources of the Upper Cretaceous Fruitland Formation in the Southern Ute Indian Reservation are estimated to total 16 billion short tons of bituminous coal in beds 2 feet thick or more. The coal-bearing Fruitland Formation underlies about 700 square miles of the Southern Ute Indian Reservation and crops out in a roughly semicircular band around the northern edge of the structural San Juan Basin. The coal beds locally dip more than 10? to the southeast along the northwestern rim of the basin.

This estimate of coal resources is based on a study of about 500 geophysical logs, mostly of oil and gas wells. Total coal resources include 15 billion short tons of identified resources, based on data points 3 miles or less apart, and about 1 billion short tons of undiscovered or hypothetical resources, based on data points more than 3 miles apart.

In this report, the coal-bearing interval is divided into three overlapping zones: lower, middle, and upper. Coal resources were estimated by aggregate thickness for each zone. The lower zone, which is southwest of a large stratigraphic rise of the Pictured Cliffs Sandstone, contains the thickest coal beds, generally in two thick beds that locally have an aggregate thickness as much as 50 feet. The lower zone contains about 28 percent of the estimated resources; in the lower zone, 6 percent of the resources are less than 500 feet beneath the surface, 10 percent of the resources are 500-2,000 feet beneath the surface, and 84 percent are more than 2,000 feet beneath the surface. The middle zone contains 22 percent of the estimated resources; in the middle zone, only 2 percent of the resources are less than 500 feet beneath the surface, 4 percent of the resources are 500-2,000 feet beneath the surface, and 94 percent are more than 2,000 feet beneath the surface. The upper zone contains about half the estimated resources, in part because it occupies about three-fourths of the area underlain by the Fruitland Formation; in the upper zone, about 2 percent of the resources are less then 500 feet beneath the surface, 11 percent are 500-2,000 feet beneath the surface, and 87 percent are more than 2,000 feet beneath the surface. In general the coal beds are thinner in the middle and upper zones than in the lower zone.

Although the coal on the Reservation is of comparatively high rank, coal in the Fruitland is generally characterized by high ash content. Mining on the Reservation has been restricted generally to small underground and strip mines within 200 feet of the surface along the edges of the San Juan Basin.