From the California DMV Web Site (http://www.dmv.ca.gov/pubs/brochures/fast_facts/ffvr29.htm)
Vehicles Purchased From Out of the Country.
“California has special requirements for vehicles imported from other countries (including Canada and Mexico). It may be very costly and in some cases impossible to modify these vehicles to meet California emission requirements and/or federal motor vehicle safety standards. For example, vehicles manufactured to be sold in Europe (gray market vehicles) less than two years old are not legal for registration or use in California”.
Bikes less than *two years old (I believe) are classified as “new” by California DMV and therefore must meet California’s stricter (than the rest of the U.S.A.) emissions (exhaust gases and fuel evaporation) standards. Even here in the U.S.A., bikes sold by California dealers are different to those sold in the other states.
* ALSO: “California law considers any vehicle with less than 7,500 miles on the odometer when acquired by a California resident or business to be a new vehicle”.
As another poster says, “Google is your friend”.