Terror of the unknown! I live within the city limits in White Plains, NY. Last year I spent the summer clearing out my small back yard of heavy ivy growth. I later noted a 2 inch hole in the ground which I cautiously covered with soil. That hole reemerged and from what I can see it is very, very deep. I am afraid of what is down there.
I have become like a child fearful of a monster in the closet. I do not like to bring harm to nature, but what is down there? What to do? Help! I take some comfort in the fact that three big men living next door.
Sounds like a mole or a shrew. Are there any mounds over the tunnel (pushed up ground or earth leading from the hole? If you walk on it the earth sinks flat again. You can flush a mole out if you see it working (tunneling on the ground) and flush it out with water from the garden hose. A shrew is like a tiny mouse and quite fast. They are feisty if messed with.
I have similar holes and my culprit (if you want to look at it that way) is a chipmunk! (Actually, by now, I believe I have a family!) I would be willing to bet you have a chippie, as well, as they love neighborhoods in cities.
My first impression from the description is a snake. After reading some of the other posts they are possible as well. Moles can be dealt with using a mole pole (that's what I call them). They are sticks you put in the ground and they beep every so often at a pitch that moles dislike. They send the signal through the ground and it supposedly runs them off. You can pick one up at a hardware store.
Chipmunks are a bit different to deal with as are the mice/shrew Lorelei mentioned. Do your neighbors have garden areas? Ask them if they have any of these holes in there yard. You might be able to figure out what it is asking them. The other advise about getting in touch with the extension office in your area is good as well. Go talk to them, ask them if there are ways you can narrow down what the pest may be. A mole makes many tunnels and you can usually walk around the yards and collapse them a little bit to verify it is a mole.
The extension office might be able to recommend different critter foods to put out that would identify which critter it is. Chipmunks and shrews may eat the same stuff but I am pretty sure a mole would eat something different as would a snake. You may be able to put some flour or baby powder around the hole in the evening. Check your local forecast and make sure it won't be raining. In the morning you may be able to see what kind of tracks are left from anything leaving and entering the hole. Take a picture of the tracks if you can and take that with you to the extension office. Of course if there are no tracks but a path going through it you know it is a snake. Then the problem would be what type. If it is a black snake you are lucky, they eat critters and other snakes keeping that population of unwanteds down.
It's probably gophers. They can dig very deep holes. If you don't want them there, drop some exlax down the holes.
Do you know your big neighbor-men? Maybe drag one to your back yard and show him the hole and see if he has any ideas. I don't know if this falls under their umbrella of knowledge, but maybe someone at your county extension office can give you some information. If you do an internet search it should be easy enough to find their number.
I hope nothing creepy is living in your hole. Good luck finding some answers!
Do your neighbors experience similar holes? Ask because critters, flowers and weeds do not grow / live only in your backyard! They are attracted to the weather and soil type you have and that probably means they are known. If your area is in White Plains, they must go somewhere for the winter. If possible, I'd wait until fall before trying to rid their hole completely. I strongly agree with the other comments that suggested contacting your extension office.
Have you tried putting a water hose down it to drown whatever it is out?
It could be any kind of nocturnal animal. Chipmunk, mole,vole, gopher. Don't be alarmed. It is just as scared of you as you are of it.