The crash happened on Frazier Road near Auberry Road.
Investigators say the driver was speeding, and they say he may have been under the influence.
Sam Hernandez and his family walked near the area where his younger sister died on Saturday.
"They were at a football game, a Sierra High football game, and that's all I know," Hernandez said. "I was in bed, I was home when I got a call from my other sister in the morning letting me know what happened."
The California Highway Patrol says at about 1:30 a.m. on Saturday, 27-year-old Cameron Conchini of Clovis was driving a Ford Mustang on Frazier Road.
Investigators say he was speeding, and they say the car crashed through a barbed wire fence before colliding into an oak tree.
The CHP says Conchini, Michelle McKeighan and Sam Hernandez's younger sister, Sandra, died in the crash.
CHP officers say the three were leaving a nearby tavern and alcohol may have been involved. Toxicology results are expected in about two weeks.
Mark Horner was in the area soon after the crash.
"I just heard the helicopter hovering over and it landed," Horner said. "And this morning I found out the accident happened."
Hernandez says his sister leaves behind four children.
"She loved her kids a lot," he said.