I've been puzzling over this name for a little while, and thought I would ask around here. The name "Mershon" is mentioned on two separate maps that I have from the Civil War. They are Confederate maps of roads and general land information around northwest Louisiana, and presumably where used during the Red River Campaign.
In one instance, a "Camp Mershon" is indicated on the map, but no camp by that name has been recorded in any history I've read (and the site itself is inaccessible/doesn't have any visible camp remnants). In another instance, a road survey map begins from a benchmark that is labeled "Mershon's commencing point of survey". Both of these points can be seen on these maps https://observablehq.com/@mradamcox/northwest-louisiana-historic-maps. Scroll down to below the maps where I have buttons to zoom you to the specific points.
Thanks for reading!
Dear Mr. Cox,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located a series titled Confederate Maps, 1861 - 1876 in the War Department Collection of Confederate Records (Record Group 109) that has been completely digitized. Also, please take a look at “A Guide to Civil War Map in the National Archives” as it may contain some helpful information.
In addition, the Library of Congress has a collection of Civil War Maps. For more information, please view their website.
We hope this information is helpful. Best of luck with your research!