Rio Grande maintenance personnel began noticing unstable ground downstream from Thistle years before the landslide occurred.
 Maintenance crews repaired the track on several occasions, but they did not fully investigate the problem.
Beginning with the remnants of Hurricane Olivia, the autumn and winter of 1982–83 featured record-breaking snow and rainfall.
As the spring thaw melted the winter snow, the mountains in the area became saturated with water.

By April 1983, track deformation was a serious issue.
On April 13, the division track master flew to Denver to explain the situation at a specially-called staff meeting.
On the same day, a Utah Highway Patrol officer struck a newly created buckle in the highway that threw him against the roof of his vehicle.
By the end of the day, a full maintenance crew was struggling to keep US‑6/US‑89 open.
All trains were limited to speeds less than 10 miles per hour (16 km/h), and were accompanied by maintenance personnel who had to continually work to keep the tracks in line.
The last train to pass through downtown Thistle was the westbound Rio Grande Zephyr, on April 14, 1983 at about 8:30 p.m. That night, both US‑6/US‑89 and the rail line were closed.
One westbound freight train that had already left Denver was turned back.
All through trains between Denver and Salt Lake City were rerouted to Union Pacific Railroad's Overland Route through Wyoming.
By April 16, the tracks were completely buried and a voluntary evacuation order was issued for the town.

On April 17, a final attempt to keep the landslide from blocking the flow of the river failed.
That day, the Utah Department of Transportation and the Rio Grande announced plans to abandon the existing transportation arteries and build new corridors.
Both the highway and railroad would be re-routed by blasting a path scaling the north wall of Spanish Fork Canyon.
The new arteries would pass the slide by dynamiting through Billies Mountain, also along the north canyon wall.
Engineers estimated the dam created by the toe of the landslide would eventually reach 200 to 300 feet (60 to 90 m) tall.
The evacuation order was changed from voluntary to mandatory.
Volunteers transported as many people and belongings as possible to the small town of Birdseye, about five miles (8 km) south.
Most residents were able to recover only a fraction of their belongings; some had less than two hours' notice before the water reached their house.
Thistle's oldest resident celebrated her 90th birthday at the evacuation center in Birdseye.
By the 18th, the waterline had reached the rooftops of the 22 previously occupied houses.
By the 19th, an entire mountain was moving at about two feet (0.6 m) per hour, and US‑6/US‑89 was buried by 50 feet (15 m) of soil.

 past the dam formed by the Thistle landslide, July 2015]]
Governor Scott Matheson requested federal aid to deal with the situation.
After a visit to the area by the director of the Federal Emergency Management Agency, U.S. president Ronald Reagan issued the first presidential disaster area declaration for the state of Utah.
The landslide eventually formed a dam that created a lake three miles (5 km) long and over 200 ft (60 m) deep.
Concerned the dam could fail, the state of Utah decided to build a tunnel to re-route the flow of the Spanish Fork (river).
The residents of downstream Spanish Fork were told to be prepared to evacuate.
Engineers estimated that if the dam failed, they would have 30 to 45 minutes notice before the water reached the city.
Rio Grande maintenance personnel began noticing unstable ground downstream from Thistle years before the landslide occurred.  Maintenance crews repaired the track on several occasions, but they did not fully investigate the problem. Beginning with the remnants of Hurricane Olivia, the autumn and winter of 1982–83 featured record-breaking snow and rainfall. As the spring thaw melted the winter snow, the mountains in the area became saturated with water.
By April 1983, track deformation was a serious issue. On April 13, the division track master flew to Denver to explain the situation at a specially-called staff meeting. On the same day, a Utah Highway Patrol officer struck a newly created buckle in the highway that threw him against the roof of his vehicle. By the end of the day, a full maintenance crew was struggling to keep US‑6/US‑89 open. All trains were limited to speeds less than 10 miles per hour (16 km/h), and were accompanied by maintenance personnel who had to continually work to keep the tracks in line. The last train to pass through downtown Thistle was the westbound Rio Grande Zephyr, on April 14, 1983 at about 8:30 p.m. That night, both US‑6/US‑89 and the rail line were closed. One westbound freight train that had already left Denver was turned back. All through trains between Denver and Salt Lake City were rerouted to Union Pacific Railroad's Overland Route through Wyoming. By April 16, the tracks were completely buried and a voluntary evacuation order was issued for the town. 
On April 17, a final attempt to keep the landslide from blocking the flow of the river failed. That day, the Utah Department of Transportation and the Rio Grande announced plans to abandon the existing transportation arteries and build new corridors. Both the highway and railroad would be re-routed by blasting a path scaling the north wall of Spanish Fork Canyon. The new arteries would pass the slide by dynamiting through Billies Mountain, also along the north canyon wall. Engineers estimated the dam created by the toe of the landslide would eventually reach 200 to 300 feet (60 to 90 m) tall. The evacuation order was changed from voluntary to mandatory. Volunteers transported as many people and belongings as possible to the small town of Birdseye, about five miles (8 km) south. Most residents were able to recover only a fraction of their belongings; some had less than two hours' notice before the water reached their house. Thistle's oldest resident celebrated her 90th birthday at the evacuation center in Birdseye. By the 18th, the waterline had reached the rooftops of the 22 previously occupied houses. By the 19th, an entire mountain was moving at about two feet (0.6 m) per hour, and US‑6/US‑89 was buried by 50 feet (15 m) of soil.
 past the dam formed by the Thistle landslide, July 2015]]
Governor Scott Matheson requested federal aid to deal with the situation. After a visit to the area by the director of the Federal Emergency Management Agency, U.S. president Ronald Reagan issued the first presidential disaster area declaration for the state of Utah. The landslide eventually formed a dam that created a lake three miles (5 km) long and over 200 ft (60 m) deep. Concerned the dam could fail, the state of Utah decided to build a tunnel to re-route the flow of the Spanish Fork (river). The residents of downstream Spanish Fork were told to be prepared to evacuate. Engineers estimated that if the dam failed, they would have 30 to 45 minutes notice before the water reached the city.
Thistle, Utah