It's in the city of Marina, at the airfield. Here's the pm scapamouche sent me...
The NASA autox is at Marina Airfield on June 8th. Take hwy 1 S to the RESERVATION rd exit in Marina, then follow the road (be careful, it turns RIGHT about 2 blocks after Denny's!) throught town. Past town, the speed limit steps up to 55, and then turn LEFT at IMJIN rd and follow the signs.