Found this on another website:
"Hey, that looks fun! I guess they are grafting them onto a standard quadbike? "
"I read about these before and yes that is what they are doing, but quad bikes are not normally street legal in the USA, ESPECIALLY in California so they are apparently doing other modifications to the vehicles to fit them within the loopholes of the laws. I am pretty sure they are all registered as KIT CARS as well since the laws governing them are much more lenient than a quad bike or a car (or a bumper car).
The ones you see in the pics are the only ones that exist, they are made by a family and just family and friends ride around in them for fun. They are not making them for other people to purchase. "