The landslide heaved houses off their foundations, toppled trees and left a gaping cavity on what had been a tree-covered hillside.
More than 100 properties were hit by the mudslide.
Seattle Times newspaper reported that many warnings had been issued about the area where the disaster.
In 1999, a report was filed to the U.S. Army Corps of Engineers highlighting “the potential for a large catastrophic failure”.
Search crew workers were forced again to briefly retreat on Monday from the western edge of the slide area after movement was detected along a 1,500-foot (460-meter) stretch of earth.
There is fear of flooding as water levels rose behind a crude dam of mud and rubble that had been dumped into the North Fork of the Stillaguamish River by the slide in an area along State Route 530, about 55 miles northeast of Seattle, in the Pacific Northwest state.
An Interstate 5 four-lane bridge over Skagit River, about 55 miles north of Seattle, Washinton collapsed at about 7 p.m. on Thursday evening sending two vehicles were into the chilly water of the river.
Rescue effort by boats and divers saved three injured people and they were taken to the Skagit Valley Hospital and the United General Hospital in Sedro-Woolley.
AP reported that authorities said it appeared nobody was killed.
U.S. National Transportation Safety Board (NSTB) is still investigating the cause of the disaster.
Anyway State Patrol Chief John R. Batiste said a semi-truck driven southbound struck the bridge just before part of it collapsed.
The freeway is a principal corridor for vehicles between Seattle and Vancouver, Canada.
The bridge was built in 1955 and the disaster raised concerns about the safety of old bridges in the United States.
In August 2007, a bridge fell into the Mississippi River in Minnesota, killing thirteen people.
AP reported that more than a quarter of Washington’s 7,840 bridges are considered structurally deficient of functionally obsolete.