The Cordero Rojo Mine extracts thermal coal from the Wyodak Seam, which ranges from approximately 55 to 70 feet in thickness.

General Geology and Coal Resources
Stratigraphic units include, in descending order recent (Quaternary age) alluvial and eolian deposits, the Eocene age Wasatch Formation (the overburden), and the Paleocene age Fort Union Formation (which contains the target coal seam).

Surficial deposits in the general analysis area include alluvial and eolian deposits and weathered Wasatch Formation. Alluvial deposits occupy the Belle Fourche River valley and the lower portions of tributary draws where they join the river.

The Eocene Wasatch Formation forms most of the overburden in the general analysis area. The boundary between the Wasatch Formation and the underlying Paleocene Fort Union Formation is not distinct. From a practical standpoint, the top of the mineable coal zone is considered as the contact between the two formations. The regional dip in this area is to the west; as a result, the overburden thickness is generally thinner to the east and increases to the west.

The Fort Union Formation is divided into three members: the Tongue River, the Lebo, and the Tullock, in descending order.

The mineable coal seams in the Powder River Basin are part of the Tongue River Member of the Fort Union. At the Cordero Rojo Mine there is one mineable coal seam. Locally, this coal zone is referred to as either the Wyodak or the Wyodak-Anderson. Up to five noncoal splits or partings occur within the seam, but they are typically local, discontinuous lenses of carbonaceous clay or shale that are less than one ft thick.

The Fort Union coal seams are subbituminous and are generally lowsulfur, low-ash coals. Typically, the coal being mined in the Powder River Basin has a higher heating value and lower sulfur content south of Gillette than north of Gillette.

Cordero began operations in 1976 and currently has a permitted mining capacity of 65 million tons per year in conjunction with the Caballo Rojo Loadout. Mining is carried out primarily by dragline operations, with truck/shovel utilized to move coal.

Coal is mined using conventional surface-mining methods and shipped from an onsite railroad loading facility to electric utilities and industrial customers in the west, midwest, and southern, United States.

The Cordero Rojo Mine uses a combination of dragline and truck shovel mining methods.

Surface mining typically involves the removal of topsoil and drilling and blasting the overburden with explosives. The overburden is then removed with draglines, trucks, shovels, and dozers. Trucks and shovels then remove the coal. The final step involves replacing the overburden and topsoil after the coal has been excavated, reestablishing vegetation into the natural habitat and making other changes designed to provide local community benefits.

The coal from mine is crushed and shipped directly from mine to the customer. Typically, no other preparation is needed for a saleable product. However, coals of various sulfur and ash contents can be mixed or “blended” to meet the specific combustion and environmental needs of customers.