There are tests to determine which state has jurisdiction and you should look into that.
For example, if the transaction/contract took place in Utah, or you've never been to the jurisdiction from whence the suit was filed, etc, you may have a solid jurisdiction argument and enough so you could laugh at that court's judgment and then force the plaintiff to come to your court upon it being found the judgment carries no legal force.
Then his option would be to present the case and its merits in your court's venue.
If the Utah court appears to have jurisdiction only due to your opposition filing there, and you haven't raised the jurisdictional argument perhaps you may be certain that Utah's jurisdiction lacking judgment may truly carry no force of law in California.
Most likely honoring the out of state judgment and Utah's Long Arming you will require a Triple Act of Congress, or similar for California to honor a Utah judgment which could get into Full Faith and Credit arguments that you might have a good chance of winning depending on the facts.
Maybe I'm completely wrong and if so, you've got some terms to research if nothing else.