DESERT CENTER, Calif. — The interstate bridge that washed out in the desert between Los Angeles and Phoenix easily withstood thousands of cars and trucks daily, but the pounding of an unusually powerful flash flood scoured away the land where the bridge was anchored, officials said Monday.
The flood severed a highway vital to the movement of people and commerce between two of the nation’s largest cities. On an average day, Interstate 10 carries about 27,000 vehicles in either direction where the bridge failed, about 50 miles west of Arizona.
Water rushing through a normally dry desert gully eroded the land around the bridge, causing one side of the eastbound span to collapse and forcing the closure of the westbound span. One motorist was injured.
While the bridge should have been fine if the flood came straight down the gully, this time it swept through at an angle that pushed the water to one bank, digging away the soil at the gully’s edge where the bridge reconnected with the road bed, California Department of Transportation spokeswoman Vanessa Wiseman said.
Caltrans was not yet sure why the flow followed that path, but such redirections are not unusual in sandy desert soil, she said.
Nine inspectors fanned out Monday to check all 44 bridges along a 20-mile stretch of I-10 after a second bridge showed signs of damage following the storm Sunday, according to Caltrans. They also planned to inspect bridges across the large swath of Southern California where the remnants of a tropical storm off Baja California dumped deluges this month.
Late Monday, Caltrans concluded that the westbound span could have a limited reopening within weeks. Work crews plan to shore it up, and eastbound traffic could then use one of its two lanes, agency spokesman Will Shuck said.
While he did not have an exact timeframe for the limited reopening, he said, ‘‘we’re certainly not talking about months.’’ Rebuilding the eastbound span would take longer.
When inspectors visited the bridge in March, they found no structural issues, said Shuck. The eastbound side was deemed “functionally obsolete,” but he said that reflected the fact it was built in 1967, when construction methods were different.
Many motorists speeding through the desert might cross the bridge without knowing. It spanned a shallow desert gully, perhaps just 60 feet wide. Such washes, as they are known, streak the desert floor and flash to life as rains are funneled into them much like tributaries can swell a river.
In a state known for weather extremes — where it may not rain for months and then rain so much that walls of water change the landscape — the loss of a short bridge was causing long lines and huge headaches.
Clarin Sepulveda, her husband, and her 16-year-old daughter were on their way back to Los Angeles from a weeklong vacation in El Paso when the bridge collapsed a mile ahead of them.
They sat on the freeway for two hours before word about what had happened started spreading among drivers. There was no cellphone service along the remote stretch of road. Sepulveda said her family and many other cars began crossing over into the 50-foot median to head back eastbound, some getting stuck in mud as rain poured down.
They spent three and a half hours trying to take two alternate state highways, only to be turned back because of flooding. They finally gave up and snagged one of the remaining motel rooms in Blythe, Calif.
“It was stressful and extremely inconvenient,” Sepulveda said Monday as the family was back on Interstate 10 after having to detour around the closure.
Remnants of the storm had dumped rain at a rate of 1.5 inches an hour. A total of 6.7 inches fell Sunday in Desert Center, National Weather Service forecaster Ken Waters said.
Showers and thunderstorms in drought-stricken southern and central California set rainfall records in what is usually a dry month.
Despite the heavy rains, California is coping overall with record drought. Regulators on Monday proposed a $1.5 million fine for a group of Central Valley farmers accused of illegally taking water during the drought.
It would be the first such fine against an individual or district with claims to water that are more than a century old, known as senior water rights holders. The action reflects the rising severity of the four-year drought, which has prompted the state to demand cutbacks from those historically sheltered from mandatory conservation.
The State Water Resources Control Board said the Byron-Bethany Irrigation District in the eastern San Francisco Bay Area illegally took water from a pumping plant even after it was warned in June enough water was not legally available.
Relying on water rights dating to 1914, the district serves 160 farming families in three counties in the agriculture-rich Central Valley and a residential community of 12,000 people.