In CA, can I use a Spousal Property Petition to cash my deceased husband's check?

I am sorry for your loss. A spousal property petition would likely work. However, if under $150,000 you could also do a probate code 13100 small estate affidavit. There are free forms on the internet for that. The key for either is that you have to be entitled to the money. That is, if there are no kids it's yours. If there are kids then it's your if it's "community property." If it's considered "separate property" you could have to share it with the kids. If not sure I would encourage you to talk to an attorney before doing a small estate affidavit. If you decide to do a spousal property petition I also would encourage you hiring an attorney as a good probate attorney makes the process much easier.