Coal seam undulations, locally called rolls, are a common but poorly understood geologic feature in underground coal mines of the Wasatch Plateau coal field of central Utah. Rolls may detract from coal mineability by: (1) creating steep grades that are difficult for mining machinery to negotiate, (2) providing low areas where mine water pools, and (3) adding diluting material which decreases coal quality. Rolls found in Skyline Mine 3 involve local, abrupt changes in elevation of the top and base of the lower O'Connor A coal seam. The change in elevation ranges from 5 to 30 ft (1.5 to 9 m) along a horizontal distance of 30-150 ft (9-46 m) and may exceed 3,000 ft (915 m) along strike. Mapping indicates the rolls are

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subparallel with a mean strike of N25°E. Changes in thickness of coal lithotypes and the coal seam itself commonly occur across the rolls.

Though a reliable model is not known which fully explains rolls, enough information exists to suggest a likely explanation. The rolls parallel the thickest portion of the Storrs Sandstone Tongue of the Starpoint Sandstone, an ancient littoral sandstone system. This and roll morphology suggest rolls are the steep sides of accretion ridge troughs which comprise the upper surface of the Storrs Sandstone tongue.

Study of the rolls has increased the reliability of their prediction, enabling the engineering staff to make appropriate changes in the mine plan in order to minimize the adverse effects on mineability.

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