Its just a cow trail. Leads off a slight hill down towards a pond. They start a second trail when the first one tough to travel on. I didn't measure these but I grabbed a stick about four foot long on one the other day and it dropped out of sight.
cfpinz-- the cows and calves try to avoid them but its a nuisance when pushing them and they get nervous. They stumble through them. I saw a baby calf step in one last week and went down over his knee. I guess it happens regularly as they pop up and keep going like nothing happened.
Mrcopier-- I wish I would see some bubbling crude come flowing out like Jed Clampett.