I'm not sure of Cooper's starting point but it was presumably south on the Texas Road perhaps near the junction of the Ft Smith-Boggy Depot Road -- this is soon after the fight at Perryville. So I'm still hanging onto the belief that Camp Johnston, if the same as "Canadian Depot (Johnson's Place)", is on the Texas Road south of North Fork Town and, as I think you suggested, on (one of) the California Road that ran along the south side of the Canadian from Ft Smith to Old Fort Holmes/Edwards at the mouth of Little River. (I believe the main road crossed to the north side of the Canadian at North Fork Town and followed the north side of the river to Edwards -- the Beale's Wagon Road -- but some maps show roads on both sides of the river.) In Dec. 1862, Lt Col Parks of the 1st Cherokee Mtd Vols wrote "I sent up a dispatch to Colonel McIntosh to fall back upon Camp Johnson south of South Canadian."
Federal reports, in Oct 1864, say that Cooper is on Canadian 65 miles south of Ft Gibson and refer to the point as "Johnson's Station". Seems 65 miles would put this point several miles south of the Canadian.
From OR, Series 1, Vol. 26, Part 2, Page 302-
HDQRS. NORTHERN SUB-DISTRICT,
Bonham, Tex., October 11, 1863.
Capt. STEPHEN D. YANCEY, A. A. A. G., Houston, Tex.:
CAPT.: Yours of the 8th instant is at hand, ...
And now, in return, permit me to give you the intelligence,
through a copy of a letter from Brig.-Gen. Cooper, that our
enemy has fallen back, and that we are advancing a little, but only to get
to where there is some forage. This is a great relief to us, and will
enable us to get ready for them whenever they come, or to help Gen.
Holmes, if he should have to fall back from Washington, Ark., in the
direction of Fulton, &c.
Most respectfully, your obedient servant,
HENRY E. McCULLOCH,
Brig.-Gen., Comdg. Northern Sub-District.
HDQRS. FIRST DIVISION, INDIAN TERRITORY,
Camp Magruder, October 9, 1863.
Brig. Gen. HENRY E. McCULLOCH,
Comdg. Sub-District of Northern Texas:
GEN.: I have to acknowledge your communication of 3d instant,
and to thank you for the information afforded and the assurance of
support by you.
The enemy is now at Fort Smith, North Fork, [Don't know what this means. Looks like a transcription error.]though not in large force.
Gen. Blunt is expected back from Kansas on the 25th instant. I
presume no important movements will be undertaken prior to his return.
I will keep vigilant watch upon the enemy, and will apprise you of all
worthy of note.
I have information that the Federal force has left Scullyville an has gone
in the direction of Fort Smith, having burned some buildings
at Scullyville and old Fort Coffee. Their travel is from Gibson to Fort
Smith, on worth [north]side of the Arkansas.
Col. Watie, with a cavalry force of Cherokees, has been sent to
intercept courier and trains on that road, and to create as much
excitement in their rear in the Cherokee Nation as possible.
I am moving this morning in the direction of North Fork, via Camp
Johnston, hear [near] Canadian, where there is an abundance of forage.
I am, general, respectfully, your obedient servant,
DOUGLAS H. COOPER,