FIrst let me say that I am terribly sorry to hear that you are in this situation. Unfortunately, California is an at will employment state. This means that your employer is allowed to change the desription of your employment for any reason that does not violate your civil rights or is in breach of contract. Thus, if you are a union employee, or if you have an employment contract that says you must be fired for cause, or that sets out your job duties, then you might have legal recourse if your employer tries to terminate you for refusing to travel. Additionally, if you believe the real reason you are being forced to travel could be related to a protected category, such as your age (40 or older), gender, race, religion, genetic information, pregnancy, national origin, creed, or disability then this would be deemed wrongful and you would have a cause of action.
Absent any of these things, it would be completely lawful for your employer to terminate your employment for your refussal to travel. That being said, if you are terminated, you would be able to file for unemployment benefits and claim, quite rightly, that you were terminated 'without cause', and seek unemployment benefits. You would not be able to seek damages but you would be able to contest the termination as being ultimately invalid.
You also could try to set up a meeting with your supervisor and explain in a calm and positive manner that you really like your job, really like working there, and explain why you would not be able to travel. If you had a doctors note stating that you could not travel due to health reasons, then you could request a reasonable accomodation under the ADA not to travel. As the essential functions of your job did not require you to travel before you would be able to keep your job as is. Under this scenario, if your employer engaged in any adverse employment action against you, you would have a claim against them for retaliation and discrimination.
I realize that the law is not entirely in your favor here and I am truly sorry to have to deliver bad news. Nonetheless, I trust that you will appreciate an accurate explanation of the law and realize that it would be unprofessional of me and unfair to you to provide you with anything less.
Please do not hesitate to let me know if you have any questions or concerns regarding the above and I will be more than happy to assist you further.
If you do not require any further assistance, I would be most grateful if you would remember to provide my service a positive rating, as this is the only way I will receive credit for assisting you.
Have a wonderful rest of your day.