Deep underneath the soil of Indiana lies some of the hardest rock around. Limestone was deposited as sediment at the bottom of an ancient ocean some 400 million years ago. Since then the ocean has disappeared, and the sediments turned into rock, and have been buried under hundreds of feet of more recent sediment. About 100 million years ago a large meteorite struck what is now northwest Indiana, creating an impact crater about 12 kilometers, or 7.25 miles, across - the fourth largest in the United States. The impact was large enough that the central area of the crater rebounded back upward. This created high ground that was not buried as deeply by the sediments that covered the rest of the crater and the Midwest.

The large impact at Kentland caused two benefits that allow humans to use the limestone there today. First, the impact was large enough that there was a rebound effect, where the central area of the impact came back up several hundred feet. Since the rock is near the surface people can access it easily without needing to remove much soil above. Secondly, the impact fractured the rock making it much easier to remove from the ground. Today, limestone from the Kentland Quarry is used for concrete in bridges and buildings, asphalt, rail ballast, and laying the foundation for roads to local windmill farms.

Sandstone is a sedimentary rock composed mostly of grains of the mineral quartz. At the Kentland Impact Structure the quartz grains are "shocked," meaning they were deformed by the energy released by a very large and sudden force. One can see that the rock is very "friable," or crumbly, which is a result of having been shocked, in this case by the impact of a large meteorite. Quartz responds to shock by fracturing and deforming along planes of weakness in the mineral's crystal structure. These features, called "planar deformation features," are only visible under a microscope.