Eastvale police responded to a report of a major-injury traffic collision at about 11:30 p.m. Sunday.
Officers found 19-year-old Eder Sid-Robles of Rialto in a crashed Honda Civic.
Sid-Robles was airlifted to Arrowhead Medical Center. He remained in critical condition Monday.
Police determined in a preliminary investigation Sid-Robles had been racing side-by-side with another vehicle at a high rate of speed westbound on Mission Blvd. near Corridor when the two vehicles collided, causing Sid-Robles to lose control of his car and crash into a tree.
The second vehicle, described as a primer-gray 2-door Honda, fled the scene. That driver was not identified and was being sought.
The investigation is ongoing, and anyone with additional information regarding this incident is asked to contact Sergeant James Woodland at (951) 955-9230.