There are nortenos in los angelas and there violent?

i just moved to los angelas right by watts and i lived here for 1 month , i moved from oakland and there the big gangs are the nortes and blacks. i was told no nortes live in la but just last week i seen a group of mexicans in red beating up some surenos and the men in red were yelling out "this northside get that stright norte for life" i have seen a few of them befor down my block and i thought they didnt live in la