Updated at 9:55 p.m. Aug. 1
The 350-acre "Volcano" fire burning near La Cresta just west of Murrieta was caused by a transportation worker mowing weeds, according to an emailed statement.
"Riverside County has been notified by fire officials that it appears the Volcano Fire was accidentally caused by a county Transportation Department worker mowing weeds alongside Tenaja Road," said Riverside County spokesperson Ray Smith.
"The county is providing its full cooperation as Fire Department officials continue their investigation and their efforts to bring the fire under control. Each year, the county works to reduce the chance of fire by clearing brush and weeds along roadsides," Smith continued.
"The fire is a tragedy for the residents whose homes are threatened and whose lives and families are being disrupted. County officials will do everything in their power to assist them."
The blaze Broadcast footage showed a large residence on fire on Valle Vista, and sheriff's radio broadcasts also indicated a second home was ablaze at 39439 Valle Vista.
The fire that was threatening the multi-million dollar homes was 75 percent contained as of 9:47 p.m. Wednesday. Three firefighters were treated for minor injuries, according to CAL FIRE/Riverside County Fire Department. Crews were expected to remain on scene throughout the night.
Early on, residents were voluntarily evacuating streets including Corte Providencia, Valle Vista and surrounding, according to Riverside County fire Capt. Roberts of Lake Elsinore Station No. 94, though no mandatory evacuations were ordered.
Red Cross opened an evacuation center at , 42200 Nighthawk Way in Murrieta, for residents affected by the fire. But the was closed as of about 6 p.m.
The "Volcano" fire was initially reported at 11:25 a.m. near Tenaja Road and Via Volcano. It spread at a moderate rate of speed, according to Melody Hendrickson, a spokesperson for CAL FIRE.
There had been potential for the fire to spread to 1,500 acres, according to reports from the scene.
Concerned residents lined the streets as structures were threatened in Tenaja, Santa Rosa West and La Cresta.
The fire jumped Valle Vista in Santa Rosa West around 1:25 p.m. At the time, homes that line Valle Vista were immediately threatened, according to resident reports from the scene received by Patch.
The area is home to many horses, and the community was on high alert. Flames were licking up against properties that overlook Sylvan Meadows, an area that is popular for hikers, mountain bikers and equestrians.
The Riverside County Sheriff's Department had been situating personnel in the event evacuations became necessary, according to reports from the scene received by Patch.
At least 233 firefighters from CAL FIRE/Riverside, CAL FIRE/San Diego, the U.S. Forest Service, Murrieta Fire Department, Pechanga Fire Department, Los Angeles County Fire Department, March ARB, San Bernardino County Fire Department, and USFS - Cleaveland were combatting the fire on the ground.
Four helicopters and six air tankers were also deployed.
Clinton Keith Road remained shut down from Avenida La Cresta to Tenaja Road, California Highway Patrol reported. The roadway was open to residents with a valid ID only.
Check back with Patch for updates.
—Toni McAllister and City News Service contributed to this report.