The state Transportation Department hopes to reopen one lane of Highway 12 near White Pass in time for weekend travel.
Spokeswoman Meagan McFadden in Yakima says traffic will be directed through the washout area by portable lights.
She says the contractor will have to bring in a lot of fill to replace ground that gave way Tuesday following heavy weekend rain.
The 500-foot long washout is three miles east of the White Pass summit. A 45-mile stretch of highway between Packwood and Naches is closed.
The department plans a temporary fix with a permanent repair next spring.