Sinkhole A crater formed when the roof of a cavern collapses; usually found in limestone areas. Surface water and precipitation that enters a sinkhole usually evaporates or infiltrates into the ground, rather than draining into a stream. Land Sites Adapted from USGS Site Types. http://wdr.water.usgs.gov/nwisgmap/help/sitetype.html ODM2 SiteType Controlled Vocabulary ODM2 Working Group A vocabulary for describing the type of a data collection Site. To some extent, these types represent the ultimate feature of interest that the site was established to measure. For example, a Stream Site was established to measure properties of a Stream.