Emergency responders were dispatched to reports of a crash near the intersection of Landana Drive and Concord Boulevard around 2:45 p.m., according to police.
Concord police Sgt. Greg Rodriguez said fire crews and police officers arrived on the scene to find one of the cars involved, a Toyota 4Runner with five occupants, turned over on its side.
A driver and passenger were inside the second car involved, he said.
Fire personnel had to extricate occupants from the Toyota 4Runner.
Four teens and two adults involved in the crash were taken to John Muir Medical Center in Walnut Creek to be treated for minor to moderate injuries, Rodriguez said.
"Seatbelts saved some lives today," the sergeant said.
He said investigators don't believe alcohol, drugs or speed were factors in the collision, but the crash remains under investigation.
Traffic near the scene of the crash was shut down for more than an hour and the roadway reopened around 4 p.m., Rodriguez said.