April 2026 Natural Mystery Answered

We received a wide range of answers to our April Natural Mystery that included a diversity of animals and a variety of behaviors. Congratulations to Ronnie Hartman, John Bauhs, and one anonymous tracker for correctly identifying both what this sign is and who left it.

These are eskers made by a plains pocket gopher (Geomys bursarius)

Our anonymous contributor notes that these cords of dirt look like the “inverted” trail system of a burrowing animal. And that is exactly what they are. John describes the process for us:

“Eskers are made in winter by an animal digging and extending underground soil tunnels into the lower layers of snow. Some of these tunnels are backfilled with soil. When the snow melts, the residual backfill material is left lying on the surface of the ground as an eskers.”

We can see that, unlike mole ridges or rooting sign, these cords of soil appear on top of last season’s plant growth—like a rope made of soil laid on the ground.

To determine who made these particular eskers, Ronnie notes: “While voles also make eskers, I think from looking at the shoes that these eskers are too wide for voles but right for pocket gophers.” John elaborated on this, writing:

“Assuming the boot toes are 5 to 6 inches wide [ed: the boots measure 4.75”], then the eskers are about 3 inches wide. Moles spend most of the winter months deep in the soil, about 3 feet down. Voles are rather small animals, and don’t need tunnels 3 inches wide, so it is less likely for them to have made these 3 inch wide eskers. Plains pocket gophers are larger than voles and could make 3 inch wide tunnels, and they spend some of their winter making tunnels close to the soil surface. Prairie pocket gophers live as far north as Bemidji where these eskers were photographed, Bemidji is in Minnesota.”

The word esker comes from the Old Irish word escir, which referred to a long, sinuous ridge of sand and gravel separating two plains. It was coined as a geological term in 1852 to refer to deposits of sediment from ancient streams flowing underneath glaciers.

Eskers are most common where snow pack reaches about three feet in the winter. With this much snow cover, a micro-climate develops underneath the snow. Insulated by the snow above, this subnivian zone (literally “under the snow”) holds a fairly constant temperature of around 32 °F even as surface temperatures drop below -20 °F. Many small mammals will spend most of the winter in this subnivian zone, creating elaborate tunnel networks, nests, and latrines. And, yes, we can sometimes find eskers made entirely out of scat.