The above is a question that's being asked repeatedly. The good news is that if you're looking to keep riding bikes in the "off season," you're hooked!
The SoCal League is set up to mimic a traditional high school spring sport in its schedule. What this means is that you can do some official "prep" work between October 15 and November 30th, the "training" season can begin on December 1st, and the "competitive" season occurs from March through May. After that finishes, the club goes dormant until the next season begins with no official League activities save for optional short duration camps in the summer. This is done for a very specific reason. As high school athletes you're still in your formative years in the sport. A very real risk is burnout if the team is on a year round training and racing schedule. The flow of the season is designed to allow your mind (and in some cases body) to take a break after the competitive season so that when you return in the fall, everything will seem fresh and exciting.
What this means is that official club activities finish on May 31st and can't start again until October 15th. What this DOESN'T mean is that you have to stop riding your bike! In fact, you can use this "off" time to train by yourselves, do fun riding, or even explore other cycling disciplines. Though the League is all about XC MTB racing, there are MANY other types of riding out there! At this point in your cycling "lives" ANY type of cycling will benefit any other type of cycling. Examples of how these other disciplines might help you as an XC MTB rider? Long road rides will help build your aerobic base, BMX will help your handling skills and pack riding, downhill will help your bike handling skills and give you confidence, track riding will help you focus and give you the ability to spin your pedals REALLY fast, cyclocross will put many of the XC skills you have to task in a shorter race, "just riding" your mountain bike will build your base and confidence --- the examples are endless!
So what do you do now? The decision is up to you! However, to help you, here are links to some resources you might investigate. One thing you might want to do is find and join a local cycling club (I'm partial to PAA, and it's also close ;-) as that is usually an inexpensive way to "link in" to the cycling scene. You can meet many experienced riders and racers and people are always scheduling rides of various types you might choose to take part in. Additionally, there are usually generous discounts that come up which make the membership fees seem VERY reasonable! I am not advocating for nor do I have any financial connection to any of the below other than one cyclocross race in Glendale that I promote as part of the SoCal Prestige series. In fact, I've only ridden on a velodrome twice and both times it was part of a cyclocross race. I also have no BMX experience save for one race in about 1978. I will, however, help to answer any questions you have!
www.paacycling.org --- Pasadena Athletic Association Cycling Club (Coach Jan, Coach Banner, Sponsor Coach Rick, Sponsor Tom Reilly, Sponsor Jerry Sanders, St. Francis Coach Bird, and I all belong to PAA)
www.lavelodrome.org --- LA Velodrome at the ADT Events Center
www.encinovelodrome.org --- Encino Velodrome. They even have a FREE beginner youth program Thursday evenings. Velodrome Director Al Nash is a PAA member.
www.sycamorebmx.com --- This is a BMX track in Simi Valley.
www.socalcross.com --- This is the SoCal Prestige Cyclocross Series. Races take place between September and January. Juniors usually race for 30-35 minutes. You CAN race on a mountain bike. Juniors usually race free if they have an annual license (I can explain that to you) or by purchasing a "one day" license for $10. Practices begin around August and take place in the Hahamonga area we practice in. Watch the website for updates.
www.racersandchasers.com --- XC MTB race series at Vail Lake.
www.usacycling.org --- This is the national governing body for cycling.
www.scnca.com --- This is the local (Southern California and Southern Nevada) chapter of USA Cycling covering our area. They maintain the calendar for all local road, track, and cyclocross races.
www.campwoodward.com --- I don't know anything about this other than the fact that, if I was your age, I would want to go HERE for camp! In addition to many other action sports, they have some pretty impressive facilities for learning advanced MTB skills!