California Code, Code of Civil Procedure - CCP § 684.220

(a) If service is made in the same manner as a summons is served under Chapter 4 (commencing with Section 413.10) of Title 5, proof of service may be made in the manner provided in Article 5 (commencing with Section 417.10) of that chapter.

(b) If service is made in the same manner as a summons is served under Section 415.10 or 415.20, proof of service may be made by affidavit of the person making the service showing the time, place, and manner of service and the facts showing that the service was made in accordance with the applicable statutory provisions. The affidavit shall recite or in other manner show the name of the person to whom the papers served were delivered and, if appropriate, the title of the person or the capacity in which the person was served.

(c) Proof of service by mail as provided in Section 684.120 may be made in the manner prescribed in Section 1013a.

(d) Proof of posting may be made by the affidavit of the person who posted the notice, showing the time and place of posting.

(e) Proof of publication may be made by the affidavit of the publisher or printer, or the foreman or principal clerk of the publisher or printer, showing the time and place of publication.

(f) Proof of service may be made by the written admission of the person served.

(g) Proof of service however made, or of posting or publication, may be made by testimonial evidence.