Depending on the year this happened, you should be able to file a California Non-Resident tax return and get your money back. You shouldn’t have earned enough for the year to hit the income limits, even in crazy California.
Since the zip code policy change, I've had many years where I had to file in ID, CA, NE due to being sent to provide support at remote sites. The NE visits were just long enough to trigger a state income tax collection. The cost to buy the NE TurboTax product was just covered by the money NE refunded. I cost me time and money. The CA visits and rates were significantly more, yet resulted in nearly full refunds...subject to taxation by ID.
The zip code policy has made me reticent to do any business travel. In addition, the travel office in the company has figured out how to deprive traveler's of per diem. They pay actuals and collect per diem. There is no longer any incentive to be frugal in travel arrangements to keep per diem above actual costs. You must use a the company credit card for all travel expenses and they pay the bill from the company office. Receipts for each expense must be uploaded. Travel has become more of a burden than an interesting part of working on a contract.