The Association of Experimental Rocketry of the Pacific, otherwise known simply as AeroPac, is a club based out of Northern California and Northern Nevada. They host 3 launches a year at Black Rock Desert, NV - Mudrock in June, Aeronaut in August, and XPRS in September. The week before XPRS, they also hold an international launch event known as ARLISS.

I joined AeroPac in 2015 and usually make it to one of their launches once every few years or so. My last time there was XPRS in 2013, and I will hopefully be at one of their launches in 2017. We'll see what happens...

While both in September and only a week apart, the main difference between XPRS and BALLS is the launch atmosphere and "vibe." XPRS is a large annual, regional club launch (much like OROC launches) with a lot of H-I-J-K-L-M impulse flights, and a very family-friendly vibe to it. BALLS on the other hand is a national event which draws attendees from all over the world, where large, experimental, and envelope-psuhing projects are flown. It is NOT a family-friendly event and is mostly attended by already-skilled fliers. Now you know why I always go to BALLS. :)

Check out the AeroPac website for lots more information on the club!