Actually, there is a standard - fifty years. But there is flexibility. At fifty years, you should consider its potential for historical value and not everything will qualify, but a lot will, like Camp 4 (actually of lot of its history is more than fifty years old). It is a tricky question and one that the NPS and other agencies have to consider carefully - it is easy to screw up when you are dealing with material in the gray zone. The best procedure is to be careful and thoughtful; check with someone responsible before taking any drastic action.

Some sites (Cape Canaveral, for example) can be deemed historically important well before they reach fifty years of age....

In my archaeological career, I have dealt with material more than 13,000 years old,, but also a lot of stuff that was much younger - Fort Bowie, AZ, 100 years of less when we worked there. The youngest material I have dealt with was a navy dive bomber that crashed off Santa Cruz Island the year I was a junior in high school. There is quite a lot that is worth preserving that is not particularly old.

I would disagree with one of WD's points. Historical material doesn't have to be associated with famous people to be significant; actually everyone's trash does have historical [/u]potential[u], at a very minimum.