Mountain highways in Riverside, San Bernardino and Orange counties were closed Thursday as a powerful storm washed out roadways or covered them in mud and debris.

Major and minor streets across the region also were closed due to flooding.

People in Idyllwild, Mountain Center and Pine Cove were essentially stranded as both highways out of the San Jacinto Mountains were closed, and they were asked to shelter in place because of the unsafe road conditions, according to the Riverside County Emergency Management Department.

Idyllwild, Mountain Center and Pine Cove asked to shelter in place due to deteriorating road conditions. Roadways are unsafe. Idyllwild School, 26700 Highway 243 in Idyllwild established as a care and reception center. (Photos courtesy Caltrans District 8) @CALFIRERRU @RSOPIOWest pic.twitter.com/asWoYzrNOT — RivCoReady (@RivCoReady) February 14, 2019

And residents across the region were warned to stay off the roads if at all possible. People who had to drive somewhere were urged to do so cautiously and pay attention to current conditions. Good sources include the Caltrans Quickmap, which has up-to-date information on crashes and road closures, and the Twitter feeds of Caltrans District 8 and the Riverside County Transportation Department, which were announcing frequent updates.

Caltrans reported multiple closures as of Thursday evening on roads it’s responsible for in Riverside and San Bernardino counties.

In the San Jacinto Mountains:

Highway 243 is closed between the 10 Freeway in Banning and Highway 74 in Mountain Center

Highway 74 is closed from Valle Vista to Lake Hemet

At the base of the mountains, Highway 111 is closed from just south of the 10 Freeway in Whitewater to the edge of Palm Springs

In the San Bernardino Mountains:

Three stretches of Highway 38 are closed, from Garnet Street (which was in danger of being washed out) in Mentone to Mill Creek; from Valley of the Falls to Seven Oaks Road; and between the Big Bear Dam and Fawnskin

Highway 18 is closed from Boulder Bay to Snow Valley

Highway 173 is closed from Highway 138 to Summit Valley Road

In the eastern San Gabriel Mountains:

Highway 2 remains closed from Big Pine to Islip Saddle

SBCO: Lots of water flow near SR-138 and I-15 in the Cajon Pass. Please, drive safely and never try to pass through rushing water. #Caltrans8 pic.twitter.com/0TcsFx1j2h — Caltrans District 8 (@Caltrans8) February 14, 2019

In the Santa Ana Mountains, the Ortega Highway was closed between Grand Avenue in Lake Elsinore and Gateway Drive in San Juan Capistrano about 2 p.m.

The Riverside County portion of the highway reopened about 4:30, while the Orange County side remained partially closed with flaggers letting vehicles through one direction at a time, according to the California Highway Patrol. The eastbound lane could be closed until 8 a.m. Friday as crews fixed damage from a rock slide.

A look at SR-74 at Grand. A big shout out to our #Caltrans8 Maintenance crews for working incredibly hard during this storm. pic.twitter.com/BHA9ErOMgu — Caltrans District 8 (@Caltrans8) February 15, 2019

Stranded vehicles had to be rescued from the closed areas on highways 38 and 74, the CHP reported.

The most severe damage in the Inland Empire appears to be on Highway 243, where a large section of the roadway washed out about noon Thursday.

Caltrans tweeted a video showing a waterfall rushing down the hillside and through a massive gap where pavement used to be.

Update: SR-243, there are two closures in place. Hurley Flats to I-10, and at Saunders Meadow. pic.twitter.com/LUHRxHYwM2 — Caltrans District 8 (@Caltrans8) February 14, 2019

Highway 74 from Valle Vista to Lake Hemet had closed earlier in the day as heavy rain started to wash out a portion of that road as well.

Caltrans said its engineers were on scene at both the 243 and 74 “to determine damages and request emergency contracts for repairs.” The final damage assessment and an estimate for how long the roads would be closed weren’t expected to be completed until Friday.

SR 74 washing out at PM 51. Travel not recommended during this storm event. #caltrans8 #TADD pic.twitter.com/fGTeyPogu5 — Caltrans District 8 (@Caltrans8) February 14, 2019

With both routes down from the mountain communities closed, a “care and reception center” was set up at Idyllwild School, 26700 Highway 243, according to the Riverside County Emergency Management Department.

Highway 111, which snake along the northern base of the steep mountainsides in the Coachella Valley, sustained damage as well. Rockslides were reported in the morning, by late afternoon part of a lane had washed out and the road was deemed compromised, and another section of highway at Snow Creek washed out Thursday evening, the CHP reported.

In the San Bernardino Mountains, Caltrans said a downbound lane of Highway 18 had been washed out from the Boulder Bay area to the Big Bear Dam. Elsewhere, crews were working to remove debris including boulders, trees and downed power lines from the roads.

SBCO: Photos from our #Caltrans8 maintenance crews in the Arctic Circle. Be advised, closure in effect from Snow Valley to Big Bear Dam. pic.twitter.com/gUx77cyrU6 — Caltrans District 8 (@Caltrans8) February 14, 2019

The CHP said via Twitter that Highway 38 from Valley of the Falls to Hatchery Road was expected to remain closed overnight, as was Highway 18 between the Big Bear Dam and Green Valley Lake Road.

The road closures and hazardous conditions Thursday prompted Mountain Transit and the Bear Valley Unified School District to cancel all public and school bus service in the Big Bear area “until further notice.” With school buses not running, parents were asked to pick up their children themselves, and to contact the school if they weren’t going to be able to.

Driving in the valleys was no pleasure Thursday, either, as numerous streets across the region flooded. Some of the larger streets that closed include portions of Highway 83 (Euclid Avenue) just west of the Prado Dam, Reche Vista Drive and Reche Canyon Road in the Moreno Valley area, Oak Valley Parkway in Beaumont, Soboba Road near San Jacinto, Deportola Road in the Temecula area, California Avenue in the Hemet area, Garnet Street in Mentone and Mt. Baldy Road in Mt. Baldy Village.

Throughout the day, emergency officials warned motorists to follow rules to keep themselves safe, including not driving on flooded streets, slowing down, leaving more space between vehicles and turning on headlines to make sure vehicles are visible to others on the road.

Please, slow down, leave room between vehicles, and stay alert. If your windshield wipers are on, turn on your headlights. And, do not try to pass through rushing water! #Caltrans8 pic.twitter.com/QkaBhOG6wX — Caltrans District 8 (@Caltrans8) February 14, 2019

Even people who stayed off the roads and rode Metrolink were affected by the storm; the agency reported numerous delays Thursday due to inclement weather.

Staff writer David Downey contributed to this report.

This story is developing. Check back for updates.