It's amusing to read that letter is almost humorous. It's an understandable policy, but I'm thinking it's slightly full of loopholes. Without knowing what is/is not an archaelogical site, you don't knowingly violate anything, which would make it difficult to prosecute in court. Geocaching is hardly vandalism, it meets not one definition of 'litter', and is a family activity that is well suited for city parks and many other areas.

While I don't intend on deliberately snubbing their rules, I do see a problem with the enforcement aspect of it.