At least 17 people were still hospitalized Monday, including at least five in critical condition.
The bus driver had major injuries, Lopez said, and the pickup driver was in extremely serious condition, said Peter Brierty, assistant county fire chief.
No one answered the door at the Scapadas Magicas office in a sprawling complex that houses more than 1,300 storage lockers and about 30 small offices.
Jordi Garcia, marketing director of Interbus Tours, said his company rented the bus from Scapadas Magicas, which supplied the driver.
Interbus offers near-daily bus tours to the western U.S. from Tijuana. Its office in a Tijuana strip mall displays photographs of some of its destinations, including Hollywood, the Las Vegas Strip and the San Diego Zoo.
There were 38 people aboard the bus that crashed, including the driver and a tour guide, Garcia said. The bus left Tijuana at 5 a.m. Sunday, with the itinerary calling for a return late that night.
He said he spoke briefly with his tour guide, who suffered bruises. She told him she heard a loud pop before the crash.
Associated Press reporters contributing to this report included Raquel Maria Dillon in San Bernardino County and Michael R. Blood, Andrew Dalton and Bob Jablon in Los Angeles. Flaccus reported from Loma Linda, Calif.