From the CARB site:
QUOTE: California regulates motorcycle aftermarket parts that have the potential to impact emissions. In most cases, the sale and use of emissions related aftermarket parts on motorcycles is prohibited unless it is either a “replacement part” as defined by California, or is a specifically authorized use of that part as reflected in an Executive Order (“EO Part”)
The California Air Resources Board (ARB) regulates aftermarket parts and has promulgated regulations that essentially place all emissions related aftermarket parts into three categories:
(First) Replacement Parts
Replacement Parts are aftermarket parts that ARB considers to be functionally equivalent to the stock part they are intended to replace, and therefore would not impact the emissions from these vehicles. These parts are appropriate for sale and use on motorcycles used on or off the public highways. For aftermarket exhaust systems and parts, there are two applicable scenarios:
(a)If the motorcycle’s stock exhaust system does not contain a catalytic converter, then an aftermarket exhaust part is a replacement part as long as the part does not remove or replace any emission control equipment originally attached to the stock exhaust system, such as the oxygen sensors.
(b)If the motorcycle’s stock exhaust system contains a catalytic converter in the manifold section of the stock exhaust system, then an aftermarket muffler positioned downstream from the catalytic converter (i.e. cat-back) is a replacement part as long as the part does not remove or replace any emission control equipment originally attached to the stock exhaust system.
(Second) Executive Order Parts
Executive Order Parts are aftermarket parts that ARB has evaluated and determined do not adversely impact emissions, and thereby are granted an Executive Order (EO), which allows the part to be sold and used on specified motorcycles. Any aftermarket exhaust system that replaces or otherwise impacts emission control equipment, including catalytic converters, requires an EO to be sold and used on a motorcycle used on or off a public highway.
(Third) Competition Use Only Parts
Competition Use only Parts may not be sold or used on a motorcycle that is used on or off the public highways other than those motorcycles used exclusively for competition. Competition Use Only Parts are aftermarket parts that replace or otherwise interfere with the operation of an emission control device, such as a catalytic converter or oxygen sensor, and may be sold and used on a motorcycle that is used only for closed course competition. END QUOTE END OF SITE INFO
So, all full systems are classified as Competition Use Only parts because they get rid of the catalytic converter, so are illegal in California (please correct me if someone knows of a full system that contains a catalytic converter).
All cat-back systems (meaning slip-ons) are legal since they qualify as "replacement parts" under CARB rules.
There aren't any issues with slip-ons being too loud because most of the muffling is done in the collector box under the frame. No slip-on will make the R3 a LOT louder. Plus, California Highway Patrol rarely, if ever, do stops, or issue citations (or fix-it tickets) for "Too Loud Pipes". Probably true as well for all local LEOS.
Now, are CHP and other LEOS actually told to check for Full Systems? Unlikely, since the budget problems are so serious in California they don't have the manpower to do this sort of enforcement. You could probably run a full system with impunity as long as it isn't "Race Track LOUD". Not advising anyone to break the laws. Just sayin'