General Geology
The strata in the Dry Fork Mine (DFM) permit area generally show northwest to north-northwest strikes and gentle westward dips. The synclinal axis trends north to northwest near the western edge of the PRB, adjacent to the Casper Arch and the Big Horn Mountains. Gentle folds occur on the eastern and northern flanks, while faults and locally overturned beds are characteristic of the much steeper western and southern flanks. The northern and eastern areas of the basin have gentle dips that seldom exceed a few degrees. Regional dips in the Gillette area are from 0.5 degrees in the surface sediments to 3 degrees in the deeper sediments toward the southwest. No major faults have been mapped in the Gillette area (Hodson et al. 1973).

The general analysis area (northern group of mines - Dry Fork, Rawhide, Buckskin, Eagle Butte, Synthetic Fuels, and Wyodak, in the part of the Northern Great Plains that includes most of northeastern Wyoming) contains the following stratigraphic units or layers (in descending order from the surface): Quaternary (most recent) deposits, the Eocene Wasatch Formation, and the Paleocene Fort Union Formation.

Surficial Geology – Quaternary deposits in the general analysis area consist of alluvium, sheetwash, colluvium, and lacustrine deposits. Quaternary deposits represent a minor component of the surficial geology within the DFM area. Exposed and weathered Wasatch Formation residuum comprises the majority of the ........

The DFM conducts open pit surface coal mine using conventional truck and loader methods. The average production rate at the DFM is approximately 6 million tons per year (Mtpy) and the maximum production rate is 15 Mtpy. A2Tr1 would not change the average production rate or the maximum production rate for the life of the mining operation.

Front-end loaders are the only loading piece of equipment utilized at Dry Fork Mine and are critical to the operation.

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