The crash occurred near the intersection of Temescal Canyon Road and Trilogy Parkway at about 10:28 p.m. Sunday, according to Cal Fire Riverside.
Authorities said Anurag Chandra, 42, of Corona, intentionally hit the Toyota Prius that the victims were in, causing the driver to lose control, veer off the road and collide into a tree just off the 15 Freeway near the entrance of the Glen Ivy Hot Springs.
The California Highway Patrol said all six teen victims were in the Prius, even though the car only has seat belts for five. Authorities are not sure if seat belts were used.
"I've been doing this 25 years and I can tell you it affects everybody. These types of incidents stay with you no matter how long you've been in law enforcement or how long you've been a first responder," said Lt. David Yokley, CHP.
The collision left three teen boys, all under the age of 18, dead and three other teenagers injured with non-life threatening injuries.
When authorities arrived, three people were trapped inside the vehicle, while another three were outside, according to Riverside officials. Three victims in the vehicle were extricated by firefighters and transported to a hospital, officials said.
One person died at the scene and two others died at a hospital, officials said. The remaining three victims sustained moderate injuries. Their exact ages were not immediately available.
Temescal Valley crash: Survivor speaks about horrifying hit-run that killed brother, 2 friends
The suspect was arrested after CHP officers found the suspect vehicle nearby, parked outside a home. The white Infiniti had front end damage.
One witness followed Chandra and helped authorities locate it, CHP Officer Juan Quintero said. Chandra was booked at the Robert Presley Detention Center on three counts of murder.
Officers have not said whether drugs or alcohol were a factor.