I used to live in your neighborhood (in RSM), so I'm familiar with the area. They're having the first round of the CMC Trans-Cal Nationals there, so it looks legit....
Here is the TranCal schedule I got off CMC's new webpage.
http://www.cmcmotocross.com/
2001 20th Annual CMC White Brothers
Trans-Cal MX Nationals
South
Round #1 Sun, Sept 9th, Irvine Lake MX, Silverado, CA 949.367.1141
Round #2 Sun, Sept 23rd, Comp Park, San Jacinto, CA 909.654.2126
Round #3 Sun, Sept 30th, Perris Raceway, Perris, CA 909.657.7441
Round #4 Sun, October 7th, Comp Park, San Jacinto, CA 909.654.2126
North
Round #1 Sat, August 11th, Riverfront Park, Marysville, CA 530.695.2727
Round #2 Sun, August 26th, Hollister Hills SVRA, Hollister, CA 775.267.4392
Round #3 Sun, Sept. 9th, Hanford Fairgrounds, Hanford, CA 559.673.8080
Round #3 Sun, Oct. 7th, Carnegie OHV, Tracy, CA 415.587.8678
Pac-NW
Round #1 Sun, August 26th, Albany SX Park, Albany, OR 541.928.4474
Round #2 Sun, Sept 23rd, Albany SX Park, Albany, OR 541.928.4474
Final Showdown
Sat & Sun, October 20th & 21st at Riverfront Park, Marysville, CA
Honda/Yamaha/Suzuki & Kawasaki Contingency available
For more info call CMC at 949.367.1141