BLYTHE, Calif. (AP) — In the second deadly recent crash involving a bus and a truck in California, four passengers were killed when their bus struck a load of metal pipes scattered across a dark highway.

Only moments before the crash early Wednesday, the pipes tumbled from a flatbed truck that jackknifed after drifting into the dirt median on Interstate 10, the main road linking Southern California and Arizona, the California Highway Patrol said.

After the bus struck the pipes on the remote stretch of desert roadway, it slid down an embankment and overturned. In addition to the four dead, at least seven passengers were seriously injured, officials said.

In the earlier crash, a big rig traveling on a northern California interstate in April smashed head-on into a charter bus carrying high school students on a university visit, killing 10 people.

Wednesday's crash occurred around 2:15 a.m. just west of Blythe, near the Arizona border, where the eastbound truck's spilled cargo obstructed both lanes in each direction. The truck carried dozens of pipes, some as long as 50 feet. The interstate was shut until about 6 p.m. Wednesday.

The bus was about three-quarters through its 800-mile trip from El Paso, Texas, to Los Angeles. Authorities believe there were 33 passengers aboard, but they were checking that against the trip manifest. Seven passengers were seriously hurt and taken to hospitals, and 14 others sought evaluation of minor injuries, according to CHP officer Jason Gerard.

Neither driver was hurt.

As the driver of the truck, whose identity was not released, tried to pass slower vehicles in an area with a 70 mph speed limit, he drifted onto the dirt shoulder and lost control, CHP Lt. Cmdr. Gustavo Guzman said.

Other drivers would have struggled to see the pipes until they were in range of a vehicle's headlights. The interstate has no lights, and the night had only a half moon.

Almost immediately, two eastbound passenger vehicles struck the pipes, though nobody was hurt in those crashes, Guzman said.

About a minute later, the bus bore down.

Richard Lee of La Mirada was sleeping in the passenger seat of an SUV that hit the pipes before the bus. He said he woke to two loud pops, got out and soon after saw the lights of what he thought was another truck approaching from the opposite direction.

"When I found out about the casualties I felt very, very lucky that I survived," Lee told KABC-TV.

The truck was operated by VG Transport and based in Rialto, east of Los Angeles. According to federal safety records, VG Transport has not been involved in any crashes reported to state officials over the past two years. Those records say the company has only one truck.

The truck passed three inspections over the past two years. After one of the inspections, a driver was not allowed to finish the trip for reasons that were not immediately clear.

The registration for the 2006 Freightliner expired in January, according to records with the California Department of Motor Vehicles. The man listed as the contact for VG Transport, Victor Esteban Galvan, could not be reached for comment. No one picked up at the listed phone number, and the voice mail box was full.

Federal records show that during a random inspection in October 2013, Galvan had an expired medical certificate, drove eight hours without a break and that his truck had been operating without undergoing periodic inspections, the Riverside Press-Enterprise reported.

The driver of the bus, operated by El Paso-Los Angeles Limousine Express Inc., had taken over the route in Phoenix, said Terri Kasinga of California Department of Transportation.

"No one has made any allegations about the bus's maintenance or the bus driver's actions being contributing factors of this accident," company President Jerry Rosenbaum said in a statement.

"Our thoughts, prayers, and unfortunately condolences go out to and for the trucker involved in the accident, occupants of any other vehicles that may have been involved, and most importantly, our passengers and driver," Rosenbaum said.

The bus company received a "satisfactory" safety rating as of its last review in February, according to federal inspection records. Other records kept by the Federal Motor Carrier Safety Administration show the company's 55 vehicles have been involved in five crashes since June 2012, one of which involved a single death.

Blythe is a city of about 25,000 people in eastern Riverside County, about 225 miles east of downtown Los Angeles.

Signs on I-10 urged drivers to find alternate routes, and authorities were diverting vehicles onto frontage roads, but traffic backed up for several miles on either side of the accident site Wednesday afternoon.

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Weber reported from Los Angeles. Associated Press writer Justin Pritchard in Los Angeles contributed to this report.