could it be an armadillo? Mine leave sorta like trenches where they dig for bugs and such. I'm a nature lover, so I let them be and just kick over the dirt, I'd rather have them then the bugs. We have tortoises that dig deep burrows as well, but I suspect you'd see those, they're big, lol.
Lori

Sounds like gophers to me. They are not easy to get rid of and they eat the roots of your grass. I knock down the mounds when I see them and water the grass in those spots.

armadillos don't live up north!!

I don't have any ideas for you, but we had a similar thing happen next to my mother's house. Mounds of dirt just appearing over-night. She called me over to try and identify what could be making the mounds, but I couldn't find any tracks or anything in the dirt around the mounds. I would carefully dismantle the mounds, scooping away inch after inch, just in case I found a tunnel I wouldn't disturb the resident too much. Each mound I ended up clearing with no signs of tunneling underneath. There were no holes, burrows, entrances or even messed up grass. It looked for all the world like someone had dumped about a 3-gal bucket worth of dirt next to her yard. But each time we dismantled a mound, the next morning there would be another. Never did figure out what was making them, but eventually they ceased to form.

Hi there! Okay so I found (against EVERY old wives tale that I have ever heard) that moles are attracted to wind pinwheels. You know, like the children's toy? I am in Orlando area, and I had a problem with a mole who I actually saw one day when pulling out of my yard in the car, rummaging around in my flower beds. I got a pinwheel, and it seemed to drive him nuts! The first day, I got it to scare him off. Clearly, that didn't work, but he seemed to be drawn to it! Each night, he tried to dig it out. My solution? Slowly moving it(the pinwheel) a little closer to my fence each night. After about a week, he seemed to have found a new home, outside of my yard. I haven't had a problem since, and its been over a year. Good luck, they are frustrating!