For the past week, we have been finding two or three of these mounds in our yard. We are on blackland prairie soil, aka "gumbo," but the mounds are of sandy soil. There is no entrance or exit hole, just this strange trough down the middle. Each mound is about 3"to 4" tall and roughly 6" long. The mounds are not clustered, but are located randomly all over the front yard and orchard area. Does anyone have any idea what they are and who makes them? All suggestions gratefully received!