Sinkholes are fairly common, due to collapsed caves, old mines or dissolving material, but the circumstances in South Dakota stand out, said Paul Santi, a professor of geological engineering at

Sinkholes are fairly common, due to collapsed caves, old mines or dissolving material, but the circumstances in South Dakota stand out, said Paul Santi, a professor of geological engineering at the Colorado School of Mines. The combination of such large sinkholes endangering so many homes makes the Hideaway Hills situation one to remember.