More than a dozen mudslides hit Burlington Northern Santa Fe tracks between Seattle and Everett during recent heavy rain.
Spokesman Gus Melonas says the largest early Tuesday at Everett covered 50 feet of track up to 15 feet deep with mud, rocks and trees.
Freight trains have been running sporadically.
Passenger trains are on hold as a safety precaution.
The Northline Sounder service was supposed to resume on Friday, but another mudslide Thursday has canceled service again.
"Barring any additional slide activity, we expect regular Northline Sounder service to resume on Monday, Nov. 26," said Sound Transit spokeswoman Kimberly Reason. "However, due to the weekend forecast of additional rainfall, we are asking riders to please check soundtransit.org for updates prior to the Monday morning commute."
Southline Sounder service between Lakewood and Seattle will operate as scheduled for the Friday special service.
Mudslides have hit tracks between Seattle and Everett dozens of times in recent winters.
Melonas says the railroad has been working to improve ditches and culverts to protect the tracks.