CAL. CCP CODE § 1011 : California Code - Section 1011

The service may be personal, by delivery to the party or attorney on whom the service is required to be made, or it may be as follows:

(a) If upon an attorney, service may be made at the attorney's office, by leaving the notice or other papers in an envelope or package clearly labeled to identify the attorney being served, with a receptionist or with a person having charge thereof. When there is no person in the office with whom the notice or papers may be left for purposes of this subdivision at the time service is to be effected, service may be made by leaving them between the hours of nine in the morning and five in the afternoon, in a conspicuous place in the office, or, if the attorney's office is not open so as to admit of that service, then service may be made by leaving the notice or papers at the attorney's residence, with some person of not less than 18 years of age, if the attorney's residence is in the same county with his or her office, and, if the attorney's residence is not known or is not in the same county with his or her office, or being in the same county it is not open, or a person 18 years of age or older cannot be found at the attorney's residence, then service may be made by putting the notice or papers, enclosed in a sealed envelope, into the post office or a mail box, subpost office, substation, or mail chute or other like facility regularly maintained by the Government of the United States directed to the attorney at his or her office, if known and otherwise to the attorney's residence, if known. If neither the attorney's office nor residence is known, service may be made by delivering the notice or papers to the address of the attorney or party of record as designated on the court papers, or by delivering the notice or papers to the clerk of the court, for the attorney.

(b) If upon a party, service shall be made in the manner specifically provided in particular cases, or, if no specific provision is made, service may be made by leaving the notice or other paper at the party's residence, between the hours of eight in the morning and six in the evening, with some person of not less than 18 years of age. If at the time of attempted service between those hours a person 18 years of age or older cannot be found at the party's residence, the notice or papers may be served by mail. If the party's residence is not known, then service may be made by delivering the notice or papers to the clerk of the court, for that party.