sentences:  On 16 September, as they were waiting for the supply train, the Confederates happened to encounter a detachment of black Union soldiers conducting hay-making operations at Flat Rock, near the confluence of Flat Rock Creek and the Grand River, about northeast of present-day Wagoner, Oklahoma and northwest of Fort Gibson.Captain E. A. Barker leading a small group of the 2nd Kansas Cavalry and a detachment from the 1st Kansas Colored Infantry, who were guarding the operation, were soon surrounded and attacked from all sides.In desperation, Barker ordered his men with horses to attempt a breakout.