I noted that General Douglas H Cooper is buried at the Fort on April 29 th 1879 in an unmarked grave with no record of his military career or of his advocacy efforts for native americans.
http://www.civilwar.org/education/history/biographies/douglas-hancock-cooper-1.html
However--
At the close/end of the war a John Johnston born abt 1785-died in 1865 a friend/frm.Indian agent to/with Cooper /likely fleed his South Canadain farm home before 1864-(Refugee's)may have sold/offered to drive- Copper -Cattle/Horses)----- Col.Phillip/Indian take-over-attempt.

Was buried there with the only marked stone at that Fort Washita park-- my math make him abt 80 years old.It's interesting how he got a friend some- Honors--when he still running the Ft.Yet a few year later--
his cause is a little more than a foot-note.