Masters Nats is at the end of august in T-Town.
Elite Nats is early october at ADT (los angeles).
There are qualifier events at most of the tracks in the US. The qualifier at Encino is this weekend, and the one at ADT is september 8-9. You have to be a 1 or 2 and qualify at one of the qualifier events to ride mass starts at elite nats. I think some lower categories can ride the time trial events (but still have to qualify).
Elite state championships are sept 15/16.
ADT and encino both have pretty active race programs, with racing pretty much every other weekend at one track or the other starting around February. This time of year is occupied by the various state and national championships and qualifiers. There's still open riding and interval training, and there will probably be practice races over the fall/winter.