Legally it has to be transferred through a California licensed firearms dealer. There is a list of them on gunbroker.com at this link:
I don't know the rules in Indiana, but you may have to take the Ruger to a licensed dealer in your area and have him send it to the licensed dealer in your son's area. Then your son can go pick it up after presenting evidence that he is legally allowed to own a firearm. Coming and going you will pay a fee to the dealer. A dealer in your area will know the rules for Indiana.
Or, you can throw it in a box and send it UPS direct to your son. But alas, that would be breaking the law. :>(