Funny, we just spent a day in Rocky Mountain National forest a few weeks ago. Very little litter anywhere, neither at the picnic area nor around Bear Lake or Nymph Lake, nor in any of the parking lots.
Spent time on the beach in Oceanside, California in April. Again, no real significant amount of trash except in a few places along the wave barriers where some had been deposited by waves -- but not in any real great amounts.
Wouldn't exactly bet on that. Had some friends who spent time in Japan, they climbed Mt Fuji and were astounded at the huge amount of litter (bags, water bottles, etc.) on the trail. They indicated it was worse than anything they had seen at US Parks.
+--------------------------------------------------------------------------------+ If you're gonna be dumb, you better be tough +--------------------------------------------------------------------------------+