I grew up there. There are absolutely gangs in SLC. I personally know and have former friends/family members active in gangs and/or currently incarcerated for gang-related crimes in SLC, including one serving life for capital murder and another doing a 12-year bid for some RICO organized crime case he caught.
Off the top of my head, there are Surenos, Nortenos, Tongan Crips, Sons of Samoa, Baby Regulators, Oriental Posse, Oriental Laos gang, Quvos, MS-13, and the Mexican Mafia has a presence there as well. They even have an episode of Gangland on the History channel specifically about Crips in SLC. It’s a city of over a million people. Just because people associate it with Mormonism doesn’t mean, in reality, there aren’t gangs there.
This is all anecdotal and based in my own personal experience, so if you want stats, I recommend looking up the Salt Lake City Metro Gang Unit. Normally I’d provide a source for you, but today I recommend looking it up yourself. I just woke up and I want breakfast.