California has a tool called Where's My Ballot which allows you to look up and receive notifications regarding the status of your ballot, including:
- When the ballot has been delivered
- The date that the voter's ballot is expected to be delivered to the voter
- If the voter's ballot is returned as undeliverable to the county elections official by the USPS
- When the voter's completed ballot has been received by the county
- Whether the voter's completed ballot has been accepted or a reason why the ballot could not be accepted and instructions of steps the voter can take in order to have the ballot accepted
- The deadline for the voter to return his or her ballot if the county has not received a voter's completed ballot by specified dates as determined by the county elections official
(From https://www.sos.ca.gov/elections/voter-registration/vote-mail#vote-by-mail)
