A party claiming title to land by mutual recognition and acquiescence must prove (1) that the boundary line between two properties was "certain, well defined, and in some fashion physically designated upon the ground,
e.g., by monuments, roadways, fence lines, etc."; (2) that the adjoining landowners, in the absence of an express boundary line agreement, manifested in good faith a mutual recognition of the designated boundary line as the true line; and (3) that mutual recognition of the boundary line continued for the period of time necessary to establish adverse possession (10 years).
Lamm v. McTighe, 72 Wash.2d 587, 593, 434 P.2d 565 (1967). These elements must be proved by clear, cogent, and convincing evidence.
Lilly v. Lynch, 88 Wash.App. 306, 316-17, 945 P.2d 727 (1997). To meet this standard of proof, the evidence must show the ultimate facts to be highly probable.
Douglas Nw., Inc. v. Bill O'Brien & Sons Constr., Inc., 64 Wash. App. 661, 678, 828 P.2d 565 (1992).