go to the bank and ask them what legal documents they need to open box. They will probably require you to go to court and get Letters of Probate appointing you executor.
The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the State of California. Responses are based solely on California law unless stated otherwise.
Go here: http://www.leginfo.ca.gov/calaw.html
Check the "Probate" box.
Read Probate Code Section 331 to see who to get into the safe deposit box, and what you can do once you have access.
If you don't know which bank it is, you've got to start there - figuring out the bank.
It's probably a bank that your father used for other accounts, although perhaps not. If you check the local banks that he used and the box is not with them, try some other banks near your father's house.
I do not know who click the thumbs down, but the probate code is very clear on how to get into the box, and "letters" are definitely not required. Take a look.