California Code, Probate Code - PROB § 16012

(a) The trustee has a duty not to delegate to others the performance of acts that the trustee can reasonably be required personally to perform and may not transfer the office of trustee to another person nor delegate the entire administration of the trust to a cotrustee or other person.

(b) In a case where a trustee has properly delegated a matter to an agent, cotrustee, or other person, the trustee has a duty to exercise general supervision over the person performing the delegated matter.

(c) This section does not apply to investment and management functions under Section 16052.