From a press release issued by CMRRA:

Twice the Excitement at Willow

You should be able to get all the motorcycle road racing you can handle this weekend, December 14-15, when Willow Springs Raceway will feature two separate motorcycle races.

WSMC will be racing the big bikes on the main track and CMRRA will be racing 50cc-80cc road race motorcycles on the Willow Kart Track.

CMRRA is where riders such as John Hopkins, Chris Ulrich, Jason Perez and many others started their careers.

Be sure to check it out.