The Off Highway, out of state Green/Red sticker regulations were quietly changed earlier this year. 

http://ohv.parks.ca.gov/pages/1234/files/OHV%20Information%20Bulletin%20-%20Non-Resident%20Red%20Sticker%20Equipment.pdf

Current Procedure: Nonresident off-highway vehicle (OHV) users, when visiting California, must have either current OHV registration from their home state or purchase a California OHV Nonresident Permit.  Current practice dictates that these visitors are not subject to California Clean Air Standards as defined in the California Code of Regulations (CCR) and can, therefore, operate their California non-compliant OHVs (red sticker motorcycles and ATVs) year round in California.

New Procedure: Enforcement of the California Air Resources Board (CARB) regulations shall be based upon the vehicle and not the residence of the owner. All OHVs that would receive an emissions noncompliant designation (Red Sticker) in California (identified by a 3 or C in the eighth digit of the VIN) may only be ridden during open Red Sticker riding seasons with a California Nonresident OHV Use Permit or an equivalent current home state registration. Riding seasons are determined by CARB and can be found at: www.ohv.parks.ca.gov/redsticker_riding.