The incident happened around 11:30 p.m. Wednesday on Sullivan Street, according to the Los Angeles County Sheriff's Department.
Deputies first responded to the area about six hours earlier regarding a call about a man in mental distress. They then learned that a man inside a home in the area was threatening to harm himself, his family members and deputies.
Lt. Daniel Vizcarra said that's when deputies notified the department's mental evaluation and crisis negotiators, who began speaking with the man. They then learned that he was possibly armed, prompting a call to the Special Enforcement Bureau, Vizcarra said.
"Once the Special Enforcement Bureau got on scene, communications continued. Eventually, the male exited the house with a high-powered rifle, which led to a deputy-involved shooting," he added.
The man, believed to be in his 40s, was struck by gunfire and pronounced dead at the scene.
It's unclear if the man fired any shots at deputies.
Two immediate family members of the man, an elderly adult and child, were inside the home when the shooting unfolded. They were not harmed.