Mont. Code Ann. § 70-19-409
Actual occupancy under claim of title not founded on instrument or judgment -- adverse
70-19-409 . Actual occupancy under claim of title not founded on instrument or judgment -- adverse. Where it appears that there has been an actual continued occupation of land under a claim of title, exclusive of any other right, but not founded upon a written instrument, judgment, or decree, the land so actually occupied and no other is deemed to have been held adversely.