I've been paying more attention to holes lately. The last couple of months I've spent some time considering differences between the western Washington mole species and their sign, perhaps that's what got me started. Regardless, while in California I spent a fair bit of time investigating holes. There are several different options down there that we don't have over here (though if you head to the east side of the cascades the options shoot up), so there was plenty to keep me occupied. Burrowing animals we found evidence of include ground squirrels, pocket gophers, woodrats, chipmunks, kangaroo rats and badgers. There was also a toad, but I'm not convinced it dug the burrow it was in (though it is my understanding the toads do dig some).
One burrow I dug out (best guess - a chipmunk burrow) had a plug of dirt an inch or two down, but once I got through that it opened into a small chamber with a few old juniper berries. The age of the berries made us think that the chamber had been abandoned. It also had a plugged tunnel leading off to the side.
I think plugged holes were one of the major themes for my hole exploration this trip. Some holes seemed relatively plug free, but many of them would seem to end except that the dirt would still be soft (while the dirt of the wall was harder) and easy to dig through until it opened up again.
When we were in the bay area there were places with numerous badger digs around. Many of them seemed to be only shallow digs, perhaps the size of my head overall, with a small throw of dirt in front of them. One we came too had a much larger dirt throw, but the hole was still the same size. This made me curious so I started digging through the dirt in the hole. It was quite soft and after I got a couple of inches down I found a side tunnel that was a hands width across - probably belonged to the critter the badger had dug out. But the badger hole kept going. I was quite curious what the deal was. Was the badger digging so far for its prey? Why weren't the other holes we found so deep? Why was it filled back in with dirt and where did the dirt come from?
As I got further in, it curved back a bit and began to open up. Eventually I had dug out as far as I could reach. We had fun sticking various body parts in the hole to see how far in we could get them.