Two people were injured in an off-road vehicle crash Sunday southwest of the city.

At about 7:30 p.m., Pima County Sheriff's Department deputies responded to a desert area at South Camino Verde, south of West Ajo Way to a report of an all-terrain vehicle crashing with a Polaris off-road vehicle, said Chief Deputy Chris Nanos.

Deputies found out that the driver of the ATV, Joshua Gradillas, 27, crashed head-on with the Polaris, which had four occupants, Nanos said.

Gradillas, who was thrown from the ATV, was taken to University of Arizona Medical Center with life-threatening injuries. He was not wearing a helmet, Nanos said.

An occupant of the Polaris was also thrown from the vehicle, and taken to UAMC with non-life threatening injuries.

The three remaining occupants in the Polaris left the scene, said Nanos.

Traffic unit detectives took over the investigation. Alcohol was a factor in the crash, said Nanos, but no further information was released.