on Aug. 14, when a group of teenage Norteño gang members pulled out a gun and shot two rival Sureños on a quiet residential street in broad daylight. Fear prompted Luis' mother, Teresa Mendez, to bring him and his sister Noela to a community meeting Tuesday night, which was organized by the San Mateo County Sheriff's Office in the wake of the shooting. "I want to know how to prevent situations like this," said Mendez, who believes there are gang members on her son's youth soccer team. Luis has told her he knows kids in his class who have already become Norteños and Sureños like their older brothers or cousins. But she didn't know her son had been offered drugs until a reporter asked him about it. It was at the Pillar Ridge mobile home community, a known gang hotspot, Luis said. "They were, like, 15 or 16," he said. "They told me they had some extra if I wanted it." More than 300 Coastsiders packed into a meeting room Tuesday for a series of Advertisement presentations that amounted to a master class on gang warfare. Locals were shocked to learn that Half Moon Bay is immersed in an all-out coastal battle between Norteños and Sureños, who have been threatening each other for months with coded graffiti in plain sight. One recent tagger painted the number "187," a reference to the California Penal Code section on murder. Retaliation is now a major concern and the Sheriff's Office has beefed up patrols. "It's a war that's going to be going on for some time, but it's a war that's worth fighting," Sheriff Greg Munks said. Officers have arrested four suspects: 21-year-old Christian Serrano DeLeon, who police believe is the gunman; Mason Paul Wessel, 19; Marco Antonio Barajas, 18; and a 17-year-old resident of Moss Beach. But even arresting every gang member in town won't make the problem disappear, officials acknowledge. They need the community's help to address the deeper crisis that's taken root when young people grow up together, go to the same schools, and end up joining rival gangs. Older gang members reach out to younger kids in middle school and offer them acceptance and a seductive feeling of power and belonging in the most vulnerable period in their young lives, according to sheriff's Deputy Mike Smyser. "They don't have much money. You can take a kid into town and buy him a cheeseburger, and you've got a friend," Smyser said. Meanwhile, their parents (mostly first-generation farmworkers) are often too distracted catch the warning signs before it's too late. They work long hours and don't notice changes in their children, Mendez said. "Latinos, we have to work a lot, but we don't really pay attention to the kids. We leave them around too much," she said. Smyser has spent 10 years tracking gang activity and juvenile crime as a school resource officer on the San Mateo County coast. He said the shooting was a major wake-up call. "I've seen fights with fists and fights with sticks. But I've never seen fights with guns," he said. Smyser has counted about 50 Norteños and 40 Sureños on the coast, two rival Mexican-American gangs that originated in the California prison system. They go by local names like Media Luna Norteños, Coastside Locos, and neighborhood-specific gangs like Moonridge Outlaws. Those numbers are modest as compared with gang sets in East Palo Alto or Redwood City, according to the Sheriff's Office, which estimates 2,000 confirmed gang members in San Mateo County affiliated with more than 50 gangs. In a small town like Half Moon Bay, it's not a mystery who's in a gang or where they congregate, said Smyser. A quick search on YouTube for one local gang turns up a video filled with youthful Norteños flashing gang signs, drinking beer and showing off their Half Moon Bay gang tattoos. By the time they reach high school, kids are already sporting gang colors: red for Norteños, blue for Sureños. Drug dealers wear purple. Half Moon Bay High School counselor Kira Gangsei said she's worked with many gang members to turn their lives around -- but it's not easy. "They don't care about school as much. Getting involved with drugs, selling drugs -- once that happens, it's harder to get them back on track," she said. The high school uses a number of classes, workshops and nonprofit programs to teach students about the dangers of gang life, drinking and unhealthy relationships. Many are led by former gang members. Now it's the community's turn. The shooting has already prompted neighborhoods to come together and form Community Watch groups, and locals have volunteered to paint over graffiti and mentor youth with the Sheriff's Activities League. "I'm not going anywhere. If it has to be me standing my ground, then yes, I'll embrace it," said Brett Bowers, a father of two who lives in the neighborhood where the shooting occurred.