Here is a link for Califonia blm rules and regs for Imperial sand dunes. You do not need a light on your whip flag for night riding, just a working RED tail light and head lights. All permits can be purchased when you arrive or online for cheaper. As for permits on the bikes, you need either your home state registration or a california out of state permit you do not need both. Only California residents are required to have a Califonia red or green sticker.
http://www.off-road.com/trucks4x4/article/...l.jsp?id=226763