"restrictive laws"? That's a first for me and I've lived in CA most of my life. So long as you've got removable mudflaps, you can do just about whatever you want. The only issues you have there are with motor swaps. Smog laws there are the strictest.
That said, I have wheeled most of America and unless you like mud and tight trees, WA can't hold a candle to CO. As far as CO goes, it's crazy beautiful and they have some of the best trails for sure but a lot of that is limited to non-winter months. CA is a big ass state with all kinds of trails, TONS OF IT that you can play on all year long. You've got the mountains like CO, you've to tight trees like WA and depending on the time of year, it can be plenty muddy in places. Of course, the one thing that WA and CO don't have are the miles and endless miles of desert that you can explore, bomb across or play hard on in the rocks. And at least for now, you've also got big dunes you can play on at the beach.