The Bureau of Mines tested a ground penetrating radar (GPR) system in the Central Florida Phosphate District to determine the feasibility of utilizing GPR technology for subsurface cavity detection. The test area is located in karst topography where sinkhole development is prevalent. State regulations require subsurface drilling of damsites to identify underground anomalies; however, this method is not totally accurate in locating subsurface cavities that could lead to sinkhole development. An electromagnetic method of identifying anomalous subsurface conditions could reduce or eliminate the possibility of dam failure due to sinkhole development. The Bureau devised a GPR system that successfully penetrated over 50 ft of overburden and gave recognizable radar return signals characteristic of a rock-cavity interface. This research at the Tuscaloosa Research Center was carried out under agreements between the Bureau of Mines, U.S. Department of the Interior, and the University of Alabama and the Florida Institute of Phosphate Research.