The crash, which occurred at about 2:45 a.m. near Auto Center Drive, shut down all lanes of the southbound 57 Freeway near the transition to the 210 Freeway and snarled traffic for hours. All lanes have since been reopened.
Witness Chad Riley came upon the scene shortly after firefighters arrived.
"There were some flames going down, but it was mostly just a lot of smoke and a lot of firemen and it was pretty intense," Riley said.
Three women were killed when their Nissan pick-up truck was rear-ended by a tractor-trailer. California Highway Patrol said the driver of the pick-up was traveling at about 5 mph along the highway when the big rig slammed into it going 55 mph.
CHP investigators believe the pick-up driver was trying to exit the freeway onto Arrow Highway safely after his truck suffered a flat tire.
The driver of the pick-up, identified as Martin Ortiz, survived. However, his wife and two sisters-in-law were trapped inside the car by two water heaters he was carrying in his truck bed.
"The frame of the Nissan pick-up truck bend downwards and it compromised the fuel tank, fuel spilled out onto the roadway, and that fuel was ignited from the frame and the fuel tank striking the roadway," described CHP Officer Steve Licon.
CHP said the women, who were not immediately identified, most likely died on impact. Officials said the women are between 30 and 55 years old.
Authorities said the big rig driver was not injured and was able to walk away from the wreck.