The crash happened early Sunday morning at Foothill Boulevard and Lime Avenue.
The four teenagers - 18-year-old Javier Contreras, 18-year-old Pedro Rivera, 18-year-old Raquel Garcia and her sister, 16-year-old Rebecca Garcia - died when their car flew out of control and slammed into a concrete bridge.
A memorial with candles, stuffed animals and flowers sits not far from the site of the crash. People stopped by to pay their respects after what police are calling one of the deadliest crashes in Fontana history.
Three of the four victims graduated from high school a few months ago.
Sergio Maldonado said he knew three of the four people who died, but he was closest with Contreras, who was the driver of the car.
"He was a good friend, had a kind heart," said Maldonado. "I decided to come down here early morning and pay my respects to him and the other three."
It was just after 1 a.m. Sunday, when somehow the driver, who was traveling eastbound on Foothill Boulevard, lost control. Police said the white 2005 Chrysler ended up crossing the center line and smashing into the concrete support for an old railroad crossing.
"It's really tough. It just goes to show for the young people out there that are driving, you need to be more responsible. It's not a game driving out there," said Maldonado.
Police said that according to witnesses, the car was traveling faster than the 45 mph speed limit.
"We don't like placing blame or trying to learn from the accident until we have actually learned what caused the accident, and at this point, we just don't know," said Fontana Police Chief Rod Jones.
Officials said there were no apparent signs of alcohol or drug-use, but it could take weeks for toxicology reports to come back. The driver had a valid license and a clean driving record.