On Big Valley Mountain (Lassen County CA) the snow was about 8″ deep. While hiking near the summit recently, Leonard and I discovered two separate runways atop the snow. Each runway consisted of two entrance/exit holes about four feet apart with tracks between the two openings. Red stains were visible in each entrance hole. The tracks only went in a single straight line between the openings.
I believe these runways on the snow surface were created by a species of Microtus, commonly knows as meadow mice, field mice or meadow voles. Although there are over a hundred species of Microtus in the United States, based on range and habitat these tracks may be those of the montane meadow mouse (Microtus montanus). Active in all seasons, meadow mice are primarily nocturnal, becoming more diurnal in the winter. They usually nest in subsurface burrows and make runways that lead to bushes or act as traffic lanes to wherever they want to go.
Along with deer mice (white footed-mice), meadow mice furnish a large majority of the small rodent tracks seen in winter. Mice always seem to be scurrying, however, when these little dark brown rodents move over white snow they are extremely vulnerable to predators. The tracks between the two openings on the runway all seem to be the double-print type trail of a running meadow mouse. (Running deer mice leave a four-print pattern.)
Meadow mice mark their territory with urine and dung. The red urine at the entrances may warn off other meadow mice or may be a method of keeping the burrow and runways under the snow clean.
Meadow mice are primarily herbivores, eating mostly forbs (green plants that are not grasses), grasses, seeds and fungi. Occasionally they will eat small insects.
Whatever small creature made these runways, they are an interesting part of the winter landscape.