Unlisted USGS reference mark in Benchmarking Posted March 3, 2011 This reference mark is likely part of a triangulation station set. If the USGS set triangulation stations like the NGS does, then the excellent article by NGS Surveyor (which is the first article pinned at the top of the benchmark forums) may help explain the set of disks used in a triangulation station. Here is the link to it. Hope it helps. http://forums.Groundspeak.com/GC/index.php?showtopic=185361 Thank you. Are USGS triangulation station markers described in some other database then?