Stone and Brush Eagle-Traps

I don't know why the text below that accompanies this drawing doesn't read: "It was common for Indians to seek high country locations, conceal themselves in a brush covered stone-lined pit structure, or as the drawing shows, a free standing brush covered stone structure. I found a couple photos that show examples of both: http://wakinguponturtleisland.blogspot.com/2013/03/eagle-traps.html