Engineering problems along the Interstate 90 development corridor in the Black Hills, SD

Approximately 80 km of Interstate 90 extends along outcrops of the Triassic Spearfish Formation between Rapid City and Spearfish, SD.  The Gypsum Spring Member is near the top of the Spearfish Formation and consists of up to 10 m of massive gypsum.  This member has formal formation status in Wyoming and forms a prominent ridge that is continuous from the Wyoming-South Dakota border southeastward for more than 50 km along I-90.  Other scattered gypsum layers are present throughout the 100- to 200-m thickness of the Spearfish Formation in the Black Hills.

Residential and industrial development is accelerating along the I-90 development corridor in the Black Hills, and much of the area is becoming urban or suburban.  Although the white gypsum layers typically are prominent and recognizable, new housing and other construction often is built on or near unstable gypsum in the Spearfish Formation, including the Gypsum Spring Member.

Because of increasing housing development pressure, it is critical that geological engineers and geologists participate in land-use decisions where karstic gypsum is involved.  Current initiatives have proposed mapping engineering hazards for the entire I-90 development corridor in the Black Hills to inform the public and local government about potential problems.


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