Weird dirt "formations" in my yard

I've got about 100 of these little piles of dirt in my yard that have popped up in the last couple of days. They are just a couple of inches across, and it definitely looks like they're "formed" some how. It doesn't appear to be scat and there isn't a hole in the ground underneath them. I'm also not noticing any insect activity around them. I've been here 6 years and this is the first time I've seen them. Anybody have any idea what they might be?