The small book "History of the Confederate Powder Works" by Col. George Washington Rains primarily covers the powder works in Augusta, Georgia. It references the limestone caves in Arkansas for their richness in nitrous earth/nitrate of lime as a salt which is convertible into saltpetre. It also states that powder-makers under military authorities were sent to Arkansas and Texas to put up the necessary powder mills for the Trans-Mississippi, which after the fall of Nashville was left necessarily left to its own resources.
I wonder if there is any record of the locations of the Arkansas Powder Mills.