1) An opening(s) (entrance and/or exit) large enough for human passage should be present permitting access from the surface down into a tunnel feature.
2) Tunnel architecture should by linear or curvilinear (i.e. an elongated passageway leading in a definable
3) Tunnel architecture (especially depth or height and width) should be large enough to accommodate adult human passage.
4) The walls and/or uncovered soil ceiling in the tunnel should have
"signatures" or markings indicating whether the tunnel had been dug by hand and/or by a machine (e.g. a backhoe).
5) There should be a compacted dirt floor (compacted by human traffic) distinguishable from surrounding non-tunnel soil which should not be that compacted.
6) The tunnel could be open (i.e. traversable and unfilled).
7) The tunnel may be naturally (i.e. natural process of erosion and soil
redeposition) or artificially (by human action)
filled in with soil. Such fill should be distinguishable from the natural soil matrix of the site in terms of color and/or by texture, and compaction (i.e.
fill would be less compact than soil forming the tunnel's walls, floor and ceiling).
8) Tunnel fill may have inclusions of: