Hi Wizard,
My sympathies regarding your nieghbors! Having been "blessed" with nieghbors with similar notions out where I live, I know what you are experiencing - and it ain't pretty, especially if you moved moved to a rural venue to enjoy the peace, quiet, and clean air.
The San Bernardino County ORV Ordinance doesn't take effect until July First, so you will need to look to other remedies for the problem until then. Trespass and disturbing the peace are a couple of strategies you can try, as is the operation of an unlicsenced ORV on public roads. Don't give up on calling law enforcement on those items; persistence counts.
Another strategy to consider is the county's dust ordinance: It is a code violation to generate dust on your propert that crosses the property line and drifts onto adjoining properties. The East Mojave AQMD has a toll free hot line you can contact to register a complaint: 1 - 800 - 635 - 4617. For best results, be prepared to give them the name and address of the party generating the dust. Getting photos or video footage of the dust crossing property lines is valuable as well, since you can't always count on the little darlings to be kicking up dust when the code enforcement officer rolls up. It's worth a try!
Meanwhile, I reccommend checking out the resources of the Community ORV Watch web site: www.orvwatch.com
If you don't already have a copy of the county ORV ordinance, you can find it posted there. A review of the ordinance will assist you in determining what options it offers for addressing the problem.
Good Luck - hang in there!
BTW, This gives me an opportunity to thank you for the long running series of posts you've made addressing the climate change / peak oil situation. Your message is important, and I apreciate the effort you've put into keeping it in front of us.
desertdude