Sometimes, a Red will dig upwards. Making inverted funnel[s]. I've stepped[ground caved in, below my foot] on a few of these over the yrs. I call those, "vent holes". Generally over/near the den chamber. One den hole, I found a couple of them on the surface. These vent holes were around an inch in diameter on the surface & hidden in the grass.
The little Red's in the above pic. Used that den [during daylight], up until late Fall. That den was on the high bank ditch along a gravel roadway. Those pups were still pretty young @ the time, a late litter.
Reds around my area, often den in the ditch's. Rarely, do they den out in the open rolling hills anymore. Coyotes in the area.