....For reasons as yet unclear, gates tend to cluster in close proximity, creating large regions of collective influence. The most massive cluster array stretches up the northeast coast of the United States, consistng of the three individual clusters in Massachusettes/Rhode Island, Maryland, and Maine. Other well-known clusters have been identified in Great Britian, the Mediterranean, and the north-central United States. This latter cluster is probably the smallest and least-known, though not lacking in eldritch activity or academic interest. The north-central, or Great Plains cluster, is comprised of an obtuse triangle of three primary locations: Ilium, South Dakota; Valley View, South Dakota; and Coburg, Nebraska. While occasional reports of gate-like activity have trickled in from other locations in Minnesota, Iowa, Nebraska, and western South Dakota, these three sites have so far been the only sources of substantial activity... --Benjamin Arliss, "Gates of Oneirology: passages to parallel planes", Miskatonic Press, 1936