There is no single answer. As stated, it depends on which state.

As a general rule, you should keep your gun in a case until you reach the area you are actually going to hunt.

That said, lets take Colorado for example. It is not legal to shoot from a vehicle even in public lands on 4 wheel drive roads. You much exit the vehicle and get a certain distance off the "road". Not sure of the distance, so you will have to look that up.

It is legal in Colorado to have your rifle out of the case in your automobile and even have ammunition in the magazine, but NOT in the chamber. However, on an ATV or UTV, you must have the gun inside a case and COMPLETELY unloaded.

So, there is no single answer to your question, because it varies depending on the situation. Looks like you got some good info on CA. But I agree you should probably try and hook up with someone who has hunted where you will be hunting