This was a very big den pipe. It has clearly been used, but just as clearly it's not in service at the moment.
This den is located near permanent water (about 100 yards from a river) and I think it might be a coyote den despite the horizontal lay of the entrance. This entrance is larger than the fox dens I have dug on in the past, and the hole stayed big as far down as I could see or feel. This is a hard-dirt area, so erosion is not much of a factor.
I remember this den from a few year back, and it was not as big a bore hole back then and held fox. Something has clearly enlarged it, and used it rather heavily.