Discussion: Is the easement a cloud on the Title and still enforceable why or why not?

John has been using a road over his neighbor Sam's property for the past twenty years. In the state where John and Sam live, the use by John of the road for twenty years gives John an easement. The road is plainly visible from an inspection of the property. Sam sells his property to Alice. Does Alice have a right to stop John from using the road? What kind of easement could John claim he has? What documentation might help resolve this issue?