Most likely it's chipmunks.

I vote for gophers. If it's gophers, I've been most successful getting them by baiting a live trap with peanut butter covered apples.

Jerger

We have had chipmunks living under our porch slab for years. They don't bother anything and are very cute. Also, toads use the chipmunk burrows, and they are beneficial.

I first noticed the chipmunks during winter a few years ago. Actually what I noticed were the tunnels they were leaving under the snow. I started just putting sunflower seeds down the holes by the slab in winter time.

I looked chipmunks up in the terrific University of Illinois Press book, "Mammals of Illinois," and it looks like they eat some insects. I have never had any trouble with them.

I have something digging in my beds too. I'm betting on oppossums or coons. One day I had planted a clump of ornamental grass, the next morning it was pulled out of its hole. I planted it again, and the next morning it was pulled out of its hole. I planted it again, and it has stayed. Holes keep appearing under a walnut tree where I planted some marigolds. New holes keep appearing every once in a while, and some marigolds were destroyed. It doesn't appear as though the plants were eaten though; just uprooted.

Thanks for all your comments. I've never seen chipmunks in the 6 mos. we've been in this house but these 2 holes are about as wide around as 2 chipmunks. This morning, the coverup that I had done last night was still in place. These holes are weird because they aren't too near the plants/roots and are pointed toward the concrete (no cracks in the foundation at that spot). I've had squirrels rip out annuals many times in the past and they didn't do that this year so that's why I was trying to see if it might be something else. I may try cutting some chicken wire and laying it under the mulch in this area because there aren't plants in the way. It's weird but now that I think about it, the holes were about as big around as a medium size squirrel body. I've also heard we have an opossum in our neighborhood so I'll keep my eyes open for that, too. If new holes appear in a different spot after I chicken wire, I'll go with the live trap idea. So far, there's been no damage to the plants. Thanks, all.

Rabbits for sure!!! We had the same problem last year. We noticed the rabbits in the yard and thought "how cute". Well, once the plants started coming up and the annuals went in the ground, we discovered that pansies are their absolute favorite meal! We have a fenced yard and thought that they came in through the gate that was often left open, so we started closing it, and then the digging began! They dug, we covered it up and they dug again. I replaced the pansies, and they ate them too, along with other things they had developed a taste for. We just gave up last year, but when they started again this season, war was decleared!
We talked about it but could not bring ourselves to poison or trap them, so we dug down about 18" all around the fence and installed a wire shield that was attached to the bottom of the fence and covered up again. It was a HUGE job, but worth it! We still see the rabbits hopping by on the way to someone elses pansies, but ours are left alone and looking beautiful. If I ever find a rabbit in my yard again, it will not be pretty!!!

Thanks everyone. Just came in from a face to face standoff with one of the snippiest rabbits I've ever encountered. I stomped my feet, chased the thing, threw a plastic hand held garden fork near him - the bugger wouldn't leave! Finally, though, I chased him out of the yard...and sadly right into our neighbor's yard. I'll be doing the wire shield routine this weekend, covering up all available holes on the 3 fenced sides of our yard and I'll be building some kind of barricade (to be determined) on the 4th side. If that doesn't work, we go the live trap route. Right now, I'm definitely not thinking "how cute"! Thanks everyone.