Hi Bryan -
WOW!!!! This is the BEST clue yet fersure!
What is the reference for this spy report anyway???
His description of Brook's cavalry brigade definitely jives with the time (Jan. 1865) when Newton's 10th Ark. Cavalry was part of Brook's command (see Magruder's 1865 report via boolean search on Cornell O.R. website using "Brooks and Dardanelle and 1865").
It seems that Newton's 10th Arkansas Cavalry, as part of Brook's cavalry brigade, may have operated out of Camp Reed during this time period.
His report also jives with the time (Winter of 1864-65) when Joseph L. Bishop and his brother were guards at CSA Camp Reed (see URL below).
Now.....all we need is some trained eye/archaeologist? to check out the area ~20 miles SSW of Arkadelphia to see if there are any earthworks, camp debris, etc.....