The Department of Financial Protection & Innovation's website includes a link to an Excel spreadsheet listing the designation of of location(s) for service of legal process on financial institutions. This listing is the result of legislation enacted a decade ago (AB 2364 (Wagner) that requires financial institutions with more than nine California branches or offices to designate one or more central locations within California for service of legal process. Financial institutions nine or fewer California branches or offices are not required to designate one or more central locations but may elect to do so. If a financial institution with more than nine California branches or offices fails to make a designation, then all the financial institutions’ branches or offices in California are deemed as central locations for service of legal process. For purposes of this law, which is codified at Section 684.115 of the Code of Civil Procedure, a financial institution includes a state or national bank, state or federal savings and loan association or credit union, or like organization, and includes a corporation engaged in a safe deposit business. Cal. Civ. Proc. Code § 680.200.
It should be noted that the DFPI's listing is a listing of locations, not agents for service of process. This information is available on the California Secretary of State's website.