What are the elements necessary to establish an agreed boundary?

In Morris v. Vossler, supra, 110 Cal.App.2d 678, 682, 243 P.2d 43, the court sets forth the five essential elements necessary to establish an agreed boundary as follows: (1) An uncertainty as to the true position of the boundary; (2) an agreement to establish a common boundary; (3) marking or building up to the agreed boundary; (4) occupation of the real property to such line; and (5) acquiescence in the line thus established for a period equal to the statute of limitations. These five points would, of course, apply only in those cases where it could not be inferred that the parties knew where the line actually was and built the fence, among other reasons, to monument the boundary line.