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<br />ecology of that region today. The potential vegetation of the region in <br />question is essentially a coniferous forest park land and shortgrass prarie <br />shrub steppe. The region was unglaciated although the margins of continen- <br />tal and alpine ice masses delimit portions of the northern and western <br />boundaries of that area. Associated with the continental ice sheets were <br />large, ephemeral proglacial lakes formed where ice advanced across river <br />courses or dry valleys to dam meltwaters highly charged with fine-grained <br />glacial sedimantes. <br />Todav's climate is one of evaporation equal to or much greater than preci- <br />pitation, Thus soils are of the pedocal type wherein salts, dominanatly- <br />calcium carbonate, are retained in the soil horizons. Where bedrock units <br />contain other salts such as sodium chloride and calcium sulfate which are <br />common in the local shales and sandstones derived from sedimentation in <br />shallow epicontinental seas that once covered the area, these salts can <br />concentrate at or near the soil surface where drainage is impeded or water <br />tables are high enough to favor evaporative wicking. IVhere the land surface <br />was disturbed by Pleistocene glaciers in the northern portion of the Ft. <br />Union formation lands in Montana and western North Dakota, the resultant <br />glacial tills derived from local rocks are now subject to severe salt build- <br />up when natural vegetation is converted to seasonal species for cropping. <br />Similarly, outside of the limits of direct glacial effects, salts now <br />deposited and distributed below the reach of shallow plant roots will move <br />upward if lands are homogenized through deep ploughing or surface mining <br />