The final major line change for the Rio Grande came as part of Utah's largest natural disaster - the landslide that dammed up the Spanish Fork and drowned Thistle, forcing relocation of the Soldier Summit line. The ground around milepost 682 was a known trouble spot. The ground had slipped here nearly every year, requiring minor maintenance to put things back in order. During the winter of 1982-1983, however, the Wasatch Mountains received a larger than normal amount of water. As a relatively mild winter, most of this moisture soaked into the soil, rather than accumulating as snow or simply running off the frozen ground. As a result, the soil was saturated when the warmer temperatures of spring came, and

While Jim Ozment, Utah Division Engineer, had noticed signs of a potential problem earlier in the spring, the first signs of immediate problems began when Bob Floyd was inspecting the track on Wednesday, 13-Apr-1983. At 0730h in the morning, he noticed the track being several inches out of line at MP 681.4. Still, railroad crews thought it would be relatively minor, and called in maintenance-of-way equipment to put the track back in line. Twelve hours later, the highway on the opposite side of the valley was also being contorted out of alignment due to the slipping mountainside. Things accelerated through the night and next morning. By the next evening US Highway 6 was closed, and the Rio Grande was soon to be. After the westbound Rio Grande Zephyr passed at 2030h on Thursday, 14-Apr-1983, the railroad was also declared closed. Sometime in the wee hours of the next morning, the railroad gave up on trying to make the slide zone passable and instead began rerouting trains via the Wyoming Union Pacific mainline.

The most pressing problem was that the slide would eventually dam up the Spanish Fork River and Soldier Creek, trapping the combined flow and possibly drowning the town of Thistle. By Sunday, 17-Apr-1983, it was apparent that no amount of bulldozers could keep the river open, and the battle was all but abandoned. The focus switched again to trying to control the new lake and ensure that the fragile new dam didn't rupture and unleash a wall of water on those downstream.

The railroad, completely severed, was already hard at work figuring out how to reroute around the new obstruction. Intermountain Technical Services, an engineering firm from Grand Junction, was called in on Monday, 18-Apr-1983, to begin surveying new routes.

On Thursday, 21-Apr-1983, plands were finalized for the new railroad alignment, as well as a diversion tunnel to establish a maximum level for the rising lake waters. Morrison-Knutsen would drill a diversion tunnel through Billies Mountain at 5180 feet, about 90 feet above the lake level on that Thursday. The level was calculated based on the lake rising at four feet per day and the amount of time MK would need to complete the project before waters rose to that point.

The new alignment was also settled. The route would involve a six mile diversion, starting at milepost 677.5, that would remain level up the south side of Billies Mountain - on the east side of the slide - and the pass through a 3000 foot tunnel, directly behind the slide itself. The tunnel would be set at 5210 feet in elevation, 30 feet above the existing diversion tunnel. The route would then drop down a 2% grade on the north side to rejoin the original alignment at 684.2.

Blasting on the diversion tunnel started around noon on 26-Apr-1983. Only 8 days later, on 4-May, the diversion tunnel had been bored all the way through the mountain. From there, a large metal pipe was attached to drop the water safely (basically without eroding the dam) along the approximately 175 feet of drop to the original river bed. Two weeks later - and only two days after the pipeline on the north side was completed - on 18-May, the lake level reached the inlet and water began flowing through the new diversion tunnel.

Only a day after the diversion tunnel was started, more M-K crews starting boring on the first of the two railroad tunnels on 27-Apr-1983. The railroad tunnel, being much larger and longer, took a significantly longer time to complete. However, the speed with which it was completed really is remarkable. All 3000 feet were completed in only a little over two months. The tunnel was holed through at 1415h on 3-Jul-1983, and by nightfall the bore was ready for track. Trackwork was complete by 1400h on 4-Jul, and at 1512h, the first train passed eastward through the tunnel. The train was Rio Grande 146, handed off from the SP at Ogden and bound for Herrington, KS. The eastbound main had been restored, and attention turned to the westbound tunnel and improving the temporary track on the connected main.

By late August, the second tunnel was complete, the first tunnel was being lined with concrete. Within a few months of that, the decision was made to drain the young lake, on account of the dam being of questionable stability. A tunnel was drilled at the base of the slide to a point under the lake, and another shaft was bored vertically to intersect it. Slowly, the nearly 200 feet of water was discharged through this drain. The tunnel continues to pass river water below the blocked canyon yet today.

Total cost of relocation was around $45 million for the railroad alone, along with the estimated $78 million in lost revenue. For a more in-depth look at the Thistle Slide, see Thistle... Focus on Disaster by Oneita Burnside Sumsion, or the Utah Geological Survey website on the slide.