The California Department of Transportation says Monday’s mudslide is 100 feet (30.5 meters) in length and up to 4 feet (1.2 meters) deep.
Nevada and California highway officials say there’s no estimate for reopening the route in the area about 50 miles southeast of Lake Tahoe.
For northbound traffic, the closure begins just north of the California agricultural inspection station.
The region has been experiencing thunderstorms and heavy rain. The National Weather Service Office in Reno issued a flood warning around 6:45 p.m. Monday.