http://galleries.burningman.org/filestore/2/9/9/6/5_e081d6a13c3c972/29965pre_4f8a5b1c63e89f8.jpg?v=2013-08-23+14%3A11%3A36
Trenching of the ring.
http://galleries.burningman.org/filestore/2/9/9/6/5_e081d6a13c3c972/29965pre_4f8a5b1c63e89f8.jpg?v=2013-08-23+14%3A11%3A36
Trenching of the ring.