The geologic structure at this site is a sinkhole known as the Crawford Sink. While many sinkholes are caused by natural processes, this particular area of subsidence is directly related to oil drilling in the Gorham Oil Field. Two oil wells, Crawford 2 and Crawford 3, were originally drilled in the center of this area. Subsidence began following removal of the wells. Improper plugging of the holes allowed groundwater to percolate through an impermeable zone (anhydrite) deep within the ground. The fresh water began to dissolve a 270-foot thick layer of salt, the Hutchinson Salt Member, within the Wellington Formation, approximately 1400 feet below the surface.
To this day, subsidence in the Crawford Sink continues at a rate of 4” to 6” per year. Numerous attempts have been made to plug the well and stop the subsidence, but no economical long term solutions are available. It has been the decision of the Kansas Department of Transportation to continually repair the section every so often. I-70 will likely continue to settle in this area until the entire thickness of salt is dissolved, although that will take hundreds of years. Numerous geophysics studies have been done on the area and there appears to be NO THREAT of a catastrophic collapse in the future.
The recent construction project included complete regrading of the roadway across the Crawford Sink and the nearby Rouback and Witt Sinks. A county road bridge over I-70 had been sinking and even twisting. Clearance issues required that it be removed during construction. Low traffic counts allowed this to happen without much inconvenience, other than the closing of I-70 for 8 hours while the bridge was demolished.
Additional sinkhole information:
Here is an article published by the Kansas Geological Survey about the seismic survey done across the area.
http://www.kgs.ku.edu/Geophysics/OFR/2008/OFR08_18/I70sink_report--OFR2008-18.pdf
Here's a link to a GigaPan image of the Sinkhole. The cache is almost visible.
http://gigapan.com/gigapans/8280?fullscreen_redirect=true
Here is what I-70 looked like prior to and during construction:
DO NOT STOP ON I-70 TO SEARCH THIS CACHE