Ft McCulloch was established after the Battle of Pea Ridge and named for Ben McCulloch who was, of course, killed in that battle. When the Confederate forces abandonned NW Arkansas, Pike moved his headquarters to the southern Choctaw Nation and constructed Ft McCulloch.
I believe the Camp McCulloch you are looking for is in the vicinity of Bentonville AR. Some members of the 15th (Northwest) Ark Volunteers enlisted there.
Ken