Its not unusual for us to stop and watch ants. This live ant tunnel is definitely something we’ve not seen before. Seth Sawyers has this to say about these ants:
It looks like a Neivamyrmex species of ant. The tunnel is to create a protected highway to move other ants, brood, and possibly the queen from one place to another. This genus of ant is commonly on the move and hardly settle into nests like other ant genera.