AT Survey Markers

[c.coyle]

Anyone have an expanation for the letters and numbers found on AT survey markers? These must be some sort of coordinates, but I've never seen this discussed anywhere.

Last weekend I encountered one climbing out of Swatara Gap in Pennsylvania stamped with "351-PA-16C". You can see it here:

http://www.henrybeaver.com/backup/AT...vey_Marker.jpg

[DebW]

I know a lilttle bit about that because I took the course to become an AT corridor monitor -- a volunteer who walks the yellow boundary line from survey marker to survey marker checking for illegal encroachment into the trail corridor. Those numbers correspond to numbers on survey maps which define the corridor. One number is probably the map number it is shown on and the other the specific marker. There are actually 3 sets of maps needed to follow the boundary. The survey maps are not to scale but list every marker and compass directions from one to the next. Other maps show the corridor to scale and all the property ownership, but don't contain contours. Finally there are contour maps. Each survey monument like the one in your picture will have 3 "witness trees" associated with it, each with three axe and yellow paint blazed marks pointing to the monument from different directions. The witness trees are on the survey map (tree type and distance and direction to the monument) so that the monument can be found later even if it gets buried.

[c.coyle]

Thanks. I'll be sure to look for the witness trees next time I see a marker.