Where do bears make their den for the winter?

While reading an online article about hibernation (yes, it IS a slow day) I found the following quote:

Technically, bears don’t hibernate. They sleep a lot in winter, but their body temperature doesn’t drop much. Also, they wake up on most days to putter about the cave. What bears do is called “daily torpor.”

Which made me wonder: Where do bears really spend their winters? I live in Pennsylvania and it is not at all uncommon for me to run across a black bear a few times a year. I just can’t believe that there are that many caves available for the number of bears out there. Do they dig their own den and if so, where do they do this?

From http://www.excite.sfu.ca/projects/exwork/best/bearden/black.htm :

In the woods?

Anywhere they want to.

Depends on the type of bear too. Grizzly’s tend to dig in high up on a north facing slope.

Black bears are not so picky, they’ll use just about anything as mentioned above.