There are bears around Crater Lake. I didn't see them but they probably saw me. The photo above shows the front paw print of a black bear which I noticed about 30 yards from my tent. Ants make small mounds of loose soil all over the place and the paw made a particularly clear impression by padding down right on top of one such mound. It happened one night when I was asleep though I do seem to remember being woken at some point by movement outside the tent so perhaps that was a nocturnal bear. 
 Fortunately there are no brown (grizzly) bears in this neck of the woods which are far more aggressive. Black bears rarely attack people and are generally very shy of human contact. There is a sensible regulation concerning backcountry camping: pitch the tent in one spot, cook in another spot away from the tent and keep food and scented items in a bear-proof canister away from both.
 A Park Ranger I spoke to last year made an interesting point when he said that if a bear takes your food it can be a death sentence for the bear.  They become addicted to human food and get bolder and bolder in trying to obtain it which may lead to them being put down. The campsite I stayed on the first few nights had a big sign at the front entrance: "There are bears in this campsite". Ironically there was perhaps more risk of encountering an aggressive bear there than when I camped out in the woods.
 Understandably several friends I spoke to were concerned about the risks associated with camping in bear country. I should think it's more dangerous to be in San Francisco (or London) where attacks by humans are quite common; also you have to exercise extreme caution if you encounter motor vehicles in their natural habitat. Statistically speaking my advice is to head out to the backcountry and take your chances with the bears: it's probably safer.
 Actually I did almost get eaten alive- by mosquitoes. For several days after the snow melted they were intense. Basically I had to be moving or in the tent; standing still or sitting in the open was not an option. At least a bear would have eaten me quick...