Investigators said they don't know how fast the cars were going, but the stretch of road where the accident took place is 30 mph.
Three passengers inside the Mustang were ejected.
Candice Ann Bustamante, 32, was one of those victims, along with a 19-year-old woman not yet identified.
Relatives said Bustamante leaves behind five children between the ages of 4 and 16.
"She was a great person," said her niece, Tanya Bustamante, as she wept at the scene of the accident. "I know everybody says that, but she was. She was a great person, a great mom. She loved her kids, loved her family, loved everything. She was full of life. We were not expecting this."
Bustamante's relatives and friends gathered Sunday to create a memorial at the base of the stone sign.
A 19-year-old man with them was also thrown from the car and is in the hospital in critical condition.
The Mustang's driver, Jesus Heredia Calixto, 18, died at the scene.
Long Beach police said the driver of the Taurus and his passenger, who are both 17 years old, were not hurt. They fled the scene but were later arrested. Their names have not been released because they are minors.
Sherrie Briggs, a resident of the neighborhood where the crash happened said she had arrived home just minutes prior.
"We were coming into the house and all of a sudden it was just like a sonic boom," Briggs said. Anyone with information is asked to call Long Beach Police Department investigators at (562) 570-7355.