Slaycation Paradise

Found in the Hicksville map. Start the Crater Run tour and head South until you reach the cliff. Now follow the cliff left as far as you can. You'll come to a red river and you should see a dead horse. Interact with the horse to receive this achievement together with the Horse Dong weapon mod and weapon. I've never been hit by a horse dong before, but have you seen those things!? Terrifying.