You're standing in a replica of an etrenchment and breastworks similar to those built north of this point in July 1877. Notice the gap between the bottom top logs. Rifle barrels could be slid through this opening while the logs provided soldiers some protection from return fire.
When Chief Looking Glass heard about the entrenchments, he called them the "soldiers corral." The soldiers hid behind the barrier of two to three logs set on top of the dirt that was thrown forward when they dug the trenches.