That's tricky! There are actually many volcanic mountains in California.

Do you have any more information about the mountain you're looking for? For example:

* Location: Is it in Northern, Central, or Southern California?

* Name: Do you remember any part of the name?

* Type of volcano: Is it a shield volcano, a stratovolcano, or a cinder cone?

* Historical significance: Is it known for a particular eruption, or is it a popular tourist destination?

Once you provide some more details, I can help you find the specific mountain you're thinking of!