Cal. Prob. Code § 1488

If before January 1, 1981, an adult has in a signed writing nominated a person to serve as guardian if a guardian is in the future appointed for such adult, such nomination shall be deemed to be a nomination of a conservator. This section applies whether or not the signed writing was executed in the same manner as a witnessed will so long as the person signing the writing had at the time the writing was signed sufficient capacity to form an intelligent preference.