San Jose has gang members (mostly Nortenos and Surenos). But they mostly bug each other. That being said, I wouldn't hangout in their neighborhoods at night, and in the case of some neighborhoods, not even in the daytime.
We also have a lot of Bikers, but they do more organized crime and all violence is mostly directed at one another and outside of town.
Anyway, fun story: When I was 16 (35 now), I trained at AKA. Every so often this guy tatted too the gills would come in and just hit the bags bareknuckled. He wasn't a gym member, he didn't pay dues, etc. I was watching him one day and said kind of out loud, "Why doesn't someone just kick him out?" My coach shushed me and told me to just stop watching him.
Later he told me he is a notorious biker known as Mr. 187. Twice he had been in fights with people in which he beat them to death but got no prison time due to self defense.
About ten years ago there was a massive funeral for some high up biker guy. Hundreds, maybe thousands of bikers came. Anyway, Mr. 187 punched the wrong guy in the nose during the funeral and got shot and killed.
I looked him up after his death. Turns out he was a mediocre pro boxer in the 80's.