Stone Structures (Maine/Alaska)

"Over the course of the day we recorded and measured 18 stone structures. Many of them have a 2 meter diameter and are half a meter in height. A few of the structures have obvious courses and were finely made."

http://lacdor.blogspot.com/2011/06/hirundo-stone-structures.html

"What makes this area even more special is the archaeological evidence of prehistoric and historic human activity. Dating back 4,000 to several hundred years ago, archaeologists are still unsure of the purposes of the large stone structures that stand along the rims of the calderas..."
http://www.nps.gov/bela/blogs/Exploring-the-southeast.htm