Seismic surveys have been used to investigate the Prairie Evaporite and Winnipegosis Formations in the vicinity of some potash mines in south-central Saskatchewan. The geophysical data, together with data from drill holes and underground mining, have revealed a complex pattern of reeflike Winnipegosis carbonate mounds. Although the carbonate mounds have been known for many years as a result of widely spaced drill holes, little was known of their size, shape, or distribution. The mounds are much smaller, more irregular, and more numerous than indicated in some earlier reports. They are flat topped, 70 to 100 m high, and 1 to 8 km broad. The distance between them ranges from 1 to 10 km or more.

Groundwater moving through the mounds in Devonian time removed some of the salt above them causing subsidence of the younger rocks. Dissolution occurred at the base of the salt. The resulting depressions are up to 30 m deep and up to the width of the mound in horizontal dimension. The dissolution probably was limited by an accumulation of insoluble material from the salt which eventually clogged the pores in the structures.

In the potash mines, local zones of intense structural or chemical alteration have been found within some depressions. Solution took place during the Middle and Late Devonian; consequently, there probably was not an oil or gas cap in the mounds at that time. Therefore, mounds with no subsidence over them may be better oil prospects, although all mounds discovered to data do have associated subsidence. However, mounds with subsidence also have structural relief in younger Devonian rocks above them and the relief may have created traps for hydrocarbon.