Salt over snow - In free ride, go from White Flats Camp to Pinwheels Ridge Camp without resorting to the chopper. (Secret)
This is similar to the other secret achievement which requires you to travel from one camp to another. The quickest way to do this is to depart White Flats Camp in free ride and then use quick travel to either a previously visited vista or livery near Pinwheels Ridge Camp. The quickest is probably the vista NW of the camp.
Or you can just drive it straight, which will take a couple of hours or so.