Better Red than Dead
Your contact, a man by the name of Hugo Davies, will issue you instructions. You must travel to the base just north of Parker and destroy it. There is a vehicle nearby, hop in and drive it to the base. Once there you'll see blue barrels and green gas tanks all over the base. Shoot them and they will explode. As you destroy the base your alert level will go up. This will cause some EDF troops to arrive. Take them out with your Assault Rifle and continue to destroy the base (with either your Sledgehammer or by shooting barrels). Once the base is destroyed hop back in your vehicle (or steal one of the EDF vehicles) and go back to the Safehouse.