I think this map was done in the spring/early summer of 1864. There's a letter in Confederate military records (as discovered in Footnote.com), Engineers, under the name Tipton Walker, who was chief of the topographical engineers in Texas, dated Houston, March 9, 1864, which includes "My principal assistant Military Engineer Capt. W. Von Rosenberg and who I [am] anxious [?] to send to Austin to procure the proper data for the Sabine reconnaissance is now here and will leave tomorrow morning."
There is also a detailed map of the lower Sabine by Caleb G. Forshey, from Williamson's Ferry to past Carter's Ferry (shows crossings from the Many, LA area to the San Augustine, TX area, now under Toledo Bend) done in September 1863, and another Forshey map of the Gaines Ferry area, also done in September 1863, both in the Augustus Forsberg military file.
William Gray Thomas's file has a map of the courier lines of SE Texas, April 12, 1864, which covers the Texas side of the river from Rusk eastward, from about the Rusk to Natchitoches line south to Burr's Ferry on the Sabine.
There are other detailed maps of the coastal areas in various files.
Vicki Betts