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Coal mine subsidence causing depressions and pits above abandoned coal mines, 10 to 15 kilometers north of Sheridan, Wyoming. The Old Monarch Mine was in operation from 1904 to 1921. Rectangular depressions, some of which are bounded by pits, are evident on the right. Some of the pits are sealed at the bottom and provide sufficient moisture to support trees. Overburden thickness is estimated to be 10 to 15 meters. The depressions occur where much of the coal has been removed and the remaining coal cannot support the weight of the overburden. Pits at the margins of the depressions commonly are caused by piping failure and the local flow of surface water to underground mines via subsidence cracks. May 1978, Frontispiece A, Geological Survey Professional paper 1164.
