5.8 earthquake rattles California’s Owens Valley, sends truck-sized boulders tumbling near Mt. Whitney

A magnitude-5.8 earthquake struck California’s Owens Valley on Wednesday morning, sending several truck-sized boulders off a mountain and causing one to slam into a tree near the trailhead of Mt. Whitney, the state’s tallest mountain.

The temblor hit the remote area off U.S. 395 at 10:40 a.m., underneath the bed of Owens Lake, just east of Mt. Whitney. There were no immediate reports of injuries or significant damage. The epicenter was about 12 miles southeast of the community of Lone Pine in Inyo County’s Owens Valley.

“We heard some big rocks coming down from a third of the way up the mountain and took off running,” said Doug Thompson, owner of the Whitney Portal Store at the Mt. Whitney trailhead, “because we didn’t know where they were going to hit.”

“At least four to five truck-size boulders knocked down some trees,” he said. “One of them slammed into a tree and then ricocheted about 50 yards through the air.”

Moments later, he said, “The air was filled with dust so thick you couldn’t see 10 yards in front of your face.”

By noon, he said, emergency responders on foot and in helicopters searched the local trails and canyons for signs of injured or stranded hikers. “I don’t believe there were any hikers on Mt. Whitney at the time the quake hit,” he said, “because the trail was closed to the public.”

The Inyo County Sheriff’s Office said the Whitney Portal area was closed and campgrounds were being evacuated due to the rock slide south of the main parking lot. Horseshoe Meadows Road was closed due to debris and rocks in the road.

According to the U.S. Geological Survey, Lone Pine, with a population of about 1,800, felt “very strong” shaking, as defined by the Modified Mercalli Intensity Scale.

In this category of shaking intensity, damage is negligible in buildings of good design and construction but may cause slight and moderate damage in well-built ordinary structures and considerable damage in poorly built or badly designed structures and may break chimneys.

The USGS said there was a 4% chance that one or more aftershocks would be larger than Wednesday morning’s magnitude-5.8 earthquake in the next week.

Weak or light shaking — which does not cause structural damage — was felt as far away as Fresno, Bakersfield, Los Angeles, San Francisco and Sacramento.

Wednesday’s quake was the most powerful to hit California since the magnitude-7.1 earthquake hit the Ridgecrest area July 5, centered roughly 50 miles to the southeast.

“I was just searching on the computer and all of a sudden, without precursor, violent shaking for two seconds, then it mellowed out into deep shakes,” said Jaylen Wright, the desk clerk at the Best Western hotel on Main Street in Lone Pine. “It was super violent at the start, almost up and down, then it went side to side.”

Wright said he felt last summer’s Ridgecrest earthquakes but that this quake was “more violent” than any he’d experienced.

The hotel has not seen power loss or significant damage, he said. A couple of items in the back office fell to the floor, and Wright said he’d heard from friends that they’d also had items fall to the ground.

“Oh my God. It was a violent, sharp shake followed by a couple of aftershocks,” said Jenifer Casteneda, a Lone Pine real estate broker. “Things fell off the wall. I ran outside of my office because it’s in an old two-story wooden building, and I was afraid it would fall on me.”

The earthquake was part of a series of temblors in the Owens Valley that started Monday evening with a magnitude-4.6 quake. There are a series of faults in the region, including the Sierra Nevada fault system, and officials are still trying to determine which faults played a role in Wednesday’s shaker, said Jen Andrews, a Caltech seismologist.

Given the earthquake’s location just north of Ridgecrest, Andrews said it was possible that “activity from the earthquake last year loaded these faults farther north and there may be some tectonic connection.”

“We have the possibility of continuing to see large earthquakes in the area,” she said. “We anticipate seeing aftershocks probably lasting weeks or months.”

There could be up to 100 magnitude-3 earthquakes in the region. A larger earthquake is less likely. There’s a 1 in 300 chance of a magnitude-7 rupture in the area.

The location of Wednesday’s earthquake was near where the larger Owens Valley earthquake occurred in 1872. That earthquake, which registered at a magnitude 7.8 or 7.9, was one of the largest on modern record in California.

Felt as far away as Los Angeles and Sacramento, that earthquake killed 27 people and destroyed 52 of the 59 houses that were there at the time.

Times staff writer Rong-Gong Lin II contributed to this report.