Jenny Durkan said Tuesday the "Hot Spot" initiative also seized nearly 14 pounds of methamphetamine as well as 28 firearms.
"These guns represent more than just guns. They represent what could've been shattered lives, shattered families and violence in the community," Durkan said.
The probe was led by federal Bureau of Alcohol, Tobacco, Firearms & Explosives (ATF) and Immigration and Customs Enforcement's Homeland Security Investigation and included local law enforcement agencies. It focused on Kent, Renton and Tukwila in addition to south Seattle.
"Had this remained in our community we can only begin to imagine how much misery this would cause," said King County Prosecutor Dan Satterberg.
Kent Police Chief Ken Thomas says such an operation is necessary "to deal with the worst of the worst gang members so our programs of prevention and intervention will have a real opportunity to be successful."
A similar initiative directed at the White Center area resulted in more than 50 arrests last year, as well as drug and gun seizures.