LAKE COUNTY, Calif. — A fire that began Saturday afternoon in the Walker Ridge area has quickly grown in size, prompting evacuations along the Lake and Colusa County lines and closing a portion of Highway 20.

The Ridge fire began at 4:26 p.m. Saturday in the area of Walker Ridge Road and Highway 20, east of Clearlake Oaks at the border shared by Lake and Colusa counties.

Cal Fire has not so far offered a possible cause for the fire, noting that it’s under investigation.

The fire is in an area that has been the site of numerous fires over the years.

Within a few hours the Ridge fire had reached 300 acres. Shortly before 9:30 p.m., air attack reported the fire was approximately 2,304 acres.

About a half hour earlier, Cal Fire had reported on its website that the fire was 2,500 acres, with no containment. That online report later was adjusted to match the report from the scene, putting containment at 10%.

As of Saturday night, Cal Fire said 50 structures were threatened — 30 in Lake County and 20 in Colusa County.

The Lake County Sheriff’s Office issued evacuation orders for several zones along Highway 20 and around Indian Valley Reservoir. The impacted zones are CLO-E070, CLO-E089, CLO-E022 and CLO-E083.

An evacuation warning was issued for CLO-E104.

Zones can be seen here.

In Colusa County, evacuation orders are in effect for Leesville Road to Leesville, Bear Valley Road to Highway 20, Wilbur Springs Road and Walker Ridge Road.

Caltrans said Highway 20 is fully closed east of Clearlake Oaks at Highway 53 in Lake County due to the fire, with no estimated time of reopening.

Officials said that Highway 20 closure extends all the way to E Street in Williams.

Other closures include Highway 16 from Brooks, Leesville Road at King Road and Leesville-Lodoga Road at Bear Valley Road.

Road conditions for state highways can be checked here.

Cal Fire said its priorities Saturday night are to hold the fire west of Bear Valley Road, south of Brim Road and at Highway 20 on the south side.

The agency said the fire is traveling northeast, but firefighters were expecting a potential wind shift at sundown that would send wind from the north.

By Saturday night, Cal Fire had quickly assigned a large contingent of resources to the incident, including 300 personnel, five helicopters, 29 engines, seven dozers, three water tenders and six crews.

Cal Fire said numerous firefighting air tankers from throughout the state were flying fire suppression missions as conditions allowed.

Radio and air traffic reported that Chinook fire helicopters were continuing to work on the incident throughout the night, with work focusing around the head of the fire and the Bear Valley Road area.

Throughout the night more private and agency dozers and water tenders were coming in. At one point, it was reported that 10 dozers were expected to arrive overnight.

Still more equipment is expected to arrive on Sunday, according to the incident command.

Email Elizabeth Larson at This email address is being protected from spambots. You need JavaScript enabled to view it.. Follow her on Twitter, @ERLarson, or Lake County News, @LakeCoNews.