Mont. Code Ann. § 77-2-105
Termination of easements
77-2-105 . Termination of easements. Whenever lands granted for any of the purposes mentioned in 77-2-101 (8) through (11) cease to be used for those purposes, the easement terminates upon notice to that effect to the person to whom the grant was made, served at the person's last-known post-office address.