Legal Question in Real Estate Law in California

The facts given are not entirely clear. By "property owner of a prescriptive easement" I assume you mean the owner of the property burdened by the easement and not the holder of the easement. In that case, I'd say the issue is whether the easement has terminated through non-use, It may have, but the ultimate answer depends upon the nature of the easement (its purpose, necessity, etc.) and an answer may require negotiation or even litigation.