BC,
One can also see it from cars and especially if one walks.  When my wife and I hike we are always picking up cans and bottles left by others.  I find it amazing that someone will carry a full container two or three miles and then not carry it empty.  I attribute the new litter problem more to new people who move here or visit.  Especially from states and countries who haven't grown-up with Oregonians awareness of the natural environment.  Soon I imagine, Oregon will become Paradise Lost.