A large rock slide closed Highway 20, the state’s longest thoroughfare, in both directions Wednesday evening at milepost 98, near Shular Road in Rockport, according to the Washington State Department of Transportation (WSDOT).

Drivers between Rockport and Marblemount are being detoured onto Highway 530, Rockport Cascade Road and Cascade River Road, WSDOT tweeted.

As of 7:10 a.m. Thursday, WSDOT had no estimate for when Highway 20, also known as the North Cascades Highway, would reopen.

Crews on the scene Wednesday night estimated the rock slide was 15 to 20 feet deep.