S. S. Graham applied for a Confederate pension from Benton County in 1906, citing his service in Co. E, Bryant's "Cherokee Arkansas Cavalry". Cooper commanded in the Indian Territory, so this might be worth looking into.

There was another S. S. Graham whose widow applied for a Confederate pension from Benton County in 1914. This was Seborn S. Graham, Jr., who served in Co. D, 2nd Arkansas Mounted Rifles, and later in Co. A, 2nd Cherokee Mounted Volunteers. He was born c1844 and died in 1898. Possibly the son of the above S. S. Graham???