cites The USGS Water-Science School Site water.usgs.gov/ https://water.usgs.gov/edu/sinkholes.html cites other human activities increase U.S. Geological Survey water.usgs.gov cites Sinkholes sinkholes U.S. Geological Survey sinkhole cites cites USGS map "Sinkholes" cites USGS's website. https://water.usgs.gov/edu/sinkholes.html U.S. Geological Survey, cites USGS Water Sciences: Sinkholes USGS cites information on sinkholes at the USGS Water Science School USGS Water Sciences: Sinkholes isn’t technically U.S. Geological Services sinkholes particular types of rock sinkholes U.S. Geological Survey U.S. Geological Survey: Sinkholes cover-subsidence sinkholes and cover-collapse sinkholes Sinkholes, from USGS Water-Science School cites USGS cites specialists from USGS explain bodies of water that are surrounded by land According to the U.S. Geological Survey, typically occur cites cites USGS (U.S. Geological Survey)