The popular name for these once-numerous but now declining landscape features associated with some Civil War sites originated through their centuries-old use as reference points in surveys and deeds. What are they?
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@LoyaltyOfDogs
This is a very difficult question because it appears to be wide opened. I zeroed in on the phrase "landscape feature' which the Texas Parks and Wildlife defines as "The land, water, vegetation, and structures that compose the characteristic landscape." Since the question stated "once numerous but now declining" I checked the description of natural landscape feature. National Geographic defines that as "A natural landscape is made up of a collection of landforms, such as mountains, hills, plains, and plateaus. Lakes, streams, soils (such as sand or clay), and natural vegetation are other features of natural landscapes." I was unable to find a particular National Park Service Survey that mentioned one "particular" feature, but I did find one
"Monocacy National Battlefield: Cultural Resources Study" By Paula S. Reed, Edith B. Wallace Page 4 footnote "While the survey were expected to be "precise," unfortunately few actually were. Survey documents often included several "degrees for variance."Trees used as boundary markers died or were felled, boundary stones were uprooted, or sometimes the course of a creek or river that served as a boundary line changed, all of which makes the recreation of an historic survey difficult to reproduce on the modem landscape." The 'boundary marker' seemed all inclusive, natural as well as man made, so I checked it online. (
Wikipedia)
Once again, natural occurrences like trees, hills, and streams are mentioned, as well as man made, such as stone fences, roads, buildings. Many of these could be classified as once numerous and now declining. A decline in natural or man made landscape features on a battlefield are caused by environmental changes, such as a gradual change in the climate, public encroachment, or prior ecological mismanagement.
Since you ask for the popular name I will submit 'boundary marker' since it appears to be inclusive of numerous landscape features that are all declining, in one way or another. I do not feel good about this answer but trees, stone fences, streams or rivers - all appear to bear equal weight in applicability, and would be covered by the boundary marker term.