What is the burden of proving adverse possession in an action to quiet title?

It is a commonplace that in an action to quiet title based on adverse possession the burden is upon the claimant to prove every necessary element: (1) The possession must be by actual occupation, open and notorious, not clandestine; (2) It must be hostile to the defendant's title; (3) It must be held under a claim of title exclusive of any other right, as one's own; (4) It must be continuous and uninterrupted for a period of five years or more prior to the commencement of the action; and (5) The taxes must be paid by the claimant. (Unger v. Mooney, 63 Cal. 586, 595, 49 Am.Rep. 100.)