The following link has a map of the firing range, the dark shaded area contained within the semi circle of smaller cans is the range(danger zone1) that is closed when small arms are being used. That semi circle of smaller cans is what is called the picket fence. The outer range is marked by larger cans much further apart and the light shaded area and the dark shaded area both would be off limits if the are shooting any thing larger than standard issued rifles. 50 caliber machine guns and anti tank weapons would closed both of those areas. Hope this helps!

http://wbsa.us/denied/range_map.jpg