[KegRiver]

I recall crawling into a bear den when I was around 12 years old.

I was surprised at how small the opening was and even more surprised at how little room there was inside, even for a skinny 12 year old kid.

Since then, I've found a number of dens, some even occupied. All were on side hills, mostly north facing or close to north facing.
And three times I've found bears denned in culverts. And know of one other.

I'm told, and have seen evidence that culverts are a death trap for bears. They do not offer enough protection from the cold and Bears that den in culverts often do not make it through winter.
As a highway maintenance worker, there was nothing worse then a frozen bear blocking a culvert during spring runoff. We had to crawl in and rig a chain on it and try to drag it out, often a next to impossible task.

Logic suggests to me that a bear den would have a huge opening, experience says otherwise. I've seen 250 pound bears crawl into den openings no bigger then a badger hole.
In fact it can be hard to know if one is looking at a bear den opening or a Wolf den. Could well be that Wolves, Coyote and Bear use dens made by one of the other two species.

I haven't seen it but the mention of bears denning under brush piles seems to be correct. When I worked in the oilfield more then one cat skinner reported rolling a bear out of it's nest in a brush pile and my dad claimed that only sows and young boars den. He claimed that the older males usually just make a nest under a blow down or brush pile.
I never had any reason to doubt dad's knowledge of all things wild. The man learned to trap before steel traps became widely available. His early trapping was done with snares and dead fall traps.
When I was born he had already been trapping for nearly forty years.
Dad was born October 10 1908.