Mont. Code Ann. § 70-20-101

An estate or interest in real property, other than an estate at will or for a term not exceeding 1 year, may not be created, granted, assigned, surrendered, or declared otherwise than by operation of law or a conveyance or other instrument in writing, subscribed by the party creating, granting, assigning, surrendering, or declaring it or by the party's lawful agent authorized by writing.