ORLAND, Calif. >> It was a busload of opportunity: young, low-income, motivated students, destined to become the first in their families to go to college, journeying from the concrete sprawl of Los Angeles to a remote redwood campus 650 miles north.

Those dreams were shattered for some Thursday in an explosive freeway crash that left 10 dead — students, chaperones and both drivers — and dozens hospitalized.

Desperate families awaited word from loved ones Friday, while investigators tried to figure out why a southbound FedEx big rig swerved across the grassy divide of California’s key artery before sideswiping a car and slamming into the tour bus, which burst into a furious blaze.

"We’re trying to think positively," said Miguel Serrato, whose twin 17-year-old sisters had set off on the adventure Thursday on separate buses. Marisol made it to their destination, Humboldt State University, but there was no word from Marisa, who had been aboard the now-gutted bus.

A sheriff’s deputy asked her father Friday morning for Marisa’s dental records, and said they believe it’s highly likely she was killed.

"We’re getting a little bit scared," Serrato said. He said his mother was booking a flight to head north.

The bus was among three Humboldt had chartered as part of its two-day Preview Plus program to bring prospective students to tour the Arcata campus, according to university officials. Before launching the event Friday, university Vice President Peg Blake’s voice broke as she asked a crowded theater for a moment of silence in honor of everyone affected by the accident.

Most survivors were injured, some with critical burns or broken limbs. Those who made it out said they scrambled through a kicked-out window. One was in flames. Those who could sprinted, others staggered, in a desperate dash to the opposite side of Interstate 5 before the vehicle exploded.

"We knew we were in major trouble," said Steven Clavijo, a high school senior from Santa Clarita, who was trying to nap when he felt the bus shake before a loud boom.

After he escaped, two more explosions followed. Clavijo and other survivors watched helplessly, knowing their peers were trapped in the inferno.

Explosions of orange flames engulfed both vehicles, and clouds of black smoke billowed into the sky until firefighters doused the fire, leaving behind scorched black hulks of metal. Bodies were draped in blankets inside the burned-out bus.

"The victims were teenage kids. A lot of them were freaked out. They were shocked. They still couldn’t grasp what happened," said Jason Wyman of the Orland Volunteer Fire Department.

Both drivers were killed, along with three adult chaperones and five teenage students, according to the California Highway Patrol, which reached the scene shortly after the 5:30 p.m. accident about 100 miles north of Sacramento. Rescuers said the bodies were mostly at the front of the bus, or outside on the ground in front of it.

Humboldt admissions counselor Arthur Arzola, 26, who worked out of Los Angeles, was among the dead. His passion for bringing kids to the university was evident on his "Meet the Counselors" webpage: Humboldt "provides all students on campus with incredible opportunities that change the world for the better."

The 44 teenagers aboard, from 31 different Southern California high schools, were participating in a program that invites prospective low-income or first-generation college students to visit Humboldt State University in far Northern California.

"The great irony here, the great sadness, is these are the very students that California needs to be successful going forward," said Timothy White, chancellor of the 23-campus California State University system, during a news conference Friday. "And so we are doubly saddened by the fact that many of them are first generation and students from low income, who have done all the right academic things and had their dream of going to Humboldt State taken away by this tragic accident."

The California Highway Patrol and the National Transportation Safety Board were investigating, but warned it could take months for them to conclude what happened.

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Joseph reported from San Francisco. Associated Press photographer Rick Pedroncelli in Orland, Associated Press writers Lisa Leff in San Francisco and Daisy Nguyen and Tami Abdollah in Los Angeles contributed to this story.