I live in the area and there was a time a few years ago when the HA's in northern CA were in the news literally just about everyday.

http://news.yahoo.com/hells-angels-violent-shines-light-gang-074756318.html

either they were getting killed off by other clubs (there was the case of a Mongol who walked into a bar in San Francisco HA's home turf and killed their club President) or they were killing each other.

HA's in CA engage in what could be considered low-intensity warfare,or disorganized flareups with the Mongols and Vagos. its usually a case where rival clubs run into each other by happenstance, in a public place,and tempers get out of control and they fight on the spot. its typically not very organized or planned out. they are however, territorial and willing to shoot or stab things out at the first sight of a rival club's patch.

are they the most powerful chapters? I can't answer that, you sure as h#ll won't see a Mongol chapter in Oakland or SF, but they do have a chapter in nearby San Jose. norcal as a whole isn't really undisputed HA territory anymore,because Mongols are there,and Vagos in sacramento and santa cruz,etc. HA's seem to be fighting an uphill battle.