The Middle Devonian Prairie Evaporite Formation is absent over a large area of South Central Saskatchewan, generally referred to as the Swift Current Platform. The absence of salts over this area may be due either to non-deposition, deposition with penecontemporaneous removal, deposition with later subsurface solution or combination of these three possibilities.

Considerations of regional structure and formation isopachs suggests that the "salt-free" area is essentially a primary feature, but that around its margins there has been solution-collapse resulting from removal of the Prairie Evaporite, mainly in post-Early Colorado time. The interpretation of fabrics of the Second Red Bed, which immediately overlies the stratigraphic position of the Prairie Evaporite, tends to support, with exceptions, the conclusions formulated from regional structural and isopach evidence.

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