History Outside my Door

I went out the other day before it turned warm to test the new cold weather clothing I bought for my trip, and came across this about 50 yards or so from my house. The ancient split-rail fence that ends at my driveway leads directly into it. It looks like it was some kind of fighting position: the stone berm gives excellent cover and concealment, and the position overlooks the entrance to the road up here from the highway. I can't say for sure that's why it was built: could be some kind of dike for rainwater runoff, or even part of a livestock pen. But I'm guessing somebody was watching movement along the trail that eventually became Hwy 33.