The crash involved 28 vehicles, including three semitrailers. Four people were killed and another six were injured, ABC News reported.
Rogel Lazaro Aguilera-Mederos, 23, of Texas, was charged with four counts of vehicular homicide, police said.
Barton, who has been homeless since 2014, said he ran down the embankment toward the wrecked vehicles and saw several vehicles on fire.
"As soon as I (saw) flames, I headed under the bridge, grabbed three or four people out of a couple cars," Barton told KDVR. "I just did what I hoped anybody would've done if I was sitting down there."