Yosemite
Apologies for being slow in posting and replying to comments recently. I spent last week on vacation in Yosemite.
In Yosemite, I heard two bears (on two different occasions), each within about 20-30 feet, but I saw neither. For some reason, this is vastly more disappointing than had I seen two bears at the same distance but not heard them. Why is that? I don't think it's just that visual information is much richer than auditory information -- for I would have been happy even with a fleeting glimpse, even if that glimpse contained no more information than I received by hearing the crashing sounds through the underbrush.
It is also quite likely that light from those bears was reflected into my eyes and made some difference to my visual experience, despite the fact that I was unable to discern its bearish source. This also is disappointing, for some reason. In some sense, I probably saw both bears -- I just didn't see that they were bears. Seeing that is just much cooler.
In about 20 miles of hiking the trails of Yosemite, I noticed only two pieces of litter. I find that quite remarkable given that some of these trails get 10,000 hikers a day.