Thru this summer, I've noticed increasing numbers of large piles of dirt in my yard - up to 2' across, about 6-10" tall, circular without signs of entry/exit. There are obvious tunnels running between some of these mounds. The dirt in the mounds has been finely "processed" - not like the lumpy dirt found in crawdad mounds. Could it be gophers? I've had mole problems before, but have never seen this type of mound. Help and THANKS.