The Denver and Rio Grande Western Railroad constructed a narrow gauge railroad over Tennessee Pass in 1881 as part of their extension to the Aspen area in order to beat the Colorado Midland's standard gauge route to the rich mining area.
 In 1890, a new standard gauge line was built from Pueblo, to Grand Junction, and jointly with the Colorado Midland Railway, a tunnel was constructed about 200 ft (61 m) below the summit.
 In 1945, the old Tennessee Pass Tunnel was replaced by a newer tunnel.
In recent times, the Rio Grande's Tennessee Pass line was the highest active mainline railroad mountain pass in the United States.
The line, now owned by the Union Pacific Railroad, is currently embargoed (the tracks are out of service but still in place).

Once the Moffat Tunnel and Dotsero Cutoff were constructed, the line through Tennessee Pass became a secondary route.
The Moffat Tunnel route had a maximum grade of 2%.
 The west side of the Tennessee Pass route has grades up to 3%.
However, the east side of the Tennessee Pass has a maximum grade of only 1.4%.

The Denver & Rio Grande's acquisition and merger to Southern Pacific Railroad (SP) in 1988 made Tennessee Pass once again the preferred transcontinental route.
SP had a central route from California through to Kansas via Donner Pass, Tennessee Pass and trackage rights on the former Missouri Pacific route from Pueblo, Colorado into Kansas.
The Moffat Tunnel route was still kept in use.

In 1996, Union Pacific Railroad (UP) bought Southern Pacific.
 UP preferred the Moffat Tunnel for routing traffic.
The last revenue train went over the Tennessee Pass on August 23, 1997.
Soon after Union Pacific ran this last train, they applied to the Surface Transportation Board for permission to abandon the line.

Currently, the line is not of much use as the former Missouri Pacific line to Pueblo has been partially abandoned so trains would have to travel from Denver, Colorado down to Pueblo, Colorado before heading west.

The 12 mi (19 km) of the Tennessee Pass line through the Royal Gorge is currently operated by the Royal Gorge Route Railroad, who operates excursion trains out of Cañon City.

On July 10, 2012, part of the old tunnel collapsed, creating a sinkhole that damaged U.S. Highway 24 and forced its temporary closure between Redcliff, Colorado and Leadville, Colorado.
 The newer tunnel was not damaged.

A report released by the Colorado Department of Transportation on September 4, 2014 stated the following about the line:
"...The Tennessee Pass line has been identified as significant to CDOT because of its potential to carry both passengers and
freight, and because it is the only existing trans-mountain alternative in Colorado to the
Moffat Tunnel line, which often runs near capacity.
The Tennessee Pass Line may be
able to be used as an alternate route as trans-mountain rail demand grows due to
increased development on the Western Slope or if the Moffat Tunnel were damaged or
closed for any reason.
Such an event would have a significant impact on Colorado,
particularly on the Western Slope, since the railroads would be forced to move freight
through Wyoming.
The Royal Gorge Route Railroad currently offers scenic, tourist rail
trips on 12 miles of the Tennessee Pass Line west of Cañon City.
No freight has been
shipped on the Tennessee Pass Line since 1997, but in relatively recent (2011)
conversations with the UP, there was no indication that UP would abandon this line in the
near future.
There have been no changes since."
On November 14, 2019, a CEO named Stefan Solow announced that he planned on buying the line using Colorado Pacific railway company to import and export grain from Kansas heading West to Dotsero and head en route to California, Nevada and Utah along the Moffat route after receiving a letter from a Colorado Pacific general counselor named William Osborn.

Union Pacific began actively discussing the sale of the line to Colorado pacific in 2019, for an amount of 10 million dollars.
However, Colorado Pacific wanted the 8.8 million dollars that the line was valued at.
After
The Denver and Rio Grande Western Railroad constructed a narrow gauge railroad over Tennessee Pass in 1881 as part of their extension to the Aspen area in order to beat the Colorado Midland's standard gauge route to the rich mining area.  In 1890, a new standard gauge line was built from Pueblo, to Grand Junction, and jointly with the Colorado Midland Railway, a tunnel was constructed about 200 ft (61 m) below the summit.  In 1945, the old Tennessee Pass Tunnel was replaced by a newer tunnel. In recent times, the Rio Grande's Tennessee Pass line was the highest active mainline railroad mountain pass in the United States. The line, now owned by the Union Pacific Railroad, is currently embargoed (the tracks are out of service but still in place).
Once the Moffat Tunnel and Dotsero Cutoff were constructed, the line through Tennessee Pass became a secondary route. The Moffat Tunnel route had a maximum grade of 2%.  The west side of the Tennessee Pass route has grades up to 3%. However, the east side of the Tennessee Pass has a maximum grade of only 1.4%.
The Denver & Rio Grande's acquisition and merger to Southern Pacific Railroad (SP) in 1988 made Tennessee Pass once again the preferred transcontinental route. SP had a central route from California through to Kansas via Donner Pass, Tennessee Pass and trackage rights on the former Missouri Pacific route from Pueblo, Colorado into Kansas. The Moffat Tunnel route was still kept in use.
In 1996, Union Pacific Railroad (UP) bought Southern Pacific.  UP preferred the Moffat Tunnel for routing traffic. The last revenue train went over the Tennessee Pass on August 23, 1997. Soon after Union Pacific ran this last train, they applied to the Surface Transportation Board for permission to abandon the line.
Currently, the line is not of much use as the former Missouri Pacific line to Pueblo has been partially abandoned so trains would have to travel from Denver, Colorado down to Pueblo, Colorado before heading west.
The 12 mi (19 km) of the Tennessee Pass line through the Royal Gorge is currently operated by the Royal Gorge Route Railroad, who operates excursion trains out of Cañon City.
On July 10, 2012, part of the old tunnel collapsed, creating a sinkhole that damaged U.S. Highway 24 and forced its temporary closure between Redcliff, Colorado and Leadville, Colorado.  The newer tunnel was not damaged.
A report released by the Colorado Department of Transportation on September 4, 2014 stated the following about the line:
"...The Tennessee Pass line has been identified as significant to CDOT because of its potential to carry both passengers and
freight, and because it is the only existing trans-mountain alternative in Colorado to the
Moffat Tunnel line, which often runs near capacity. The Tennessee Pass Line may be
able to be used as an alternate route as trans-mountain rail demand grows due to
increased development on the Western Slope or if the Moffat Tunnel were damaged or
closed for any reason. Such an event would have a significant impact on Colorado,
particularly on the Western Slope, since the railroads would be forced to move freight
through Wyoming. The Royal Gorge Route Railroad currently offers scenic, tourist rail
trips on 12 miles of the Tennessee Pass Line west of Cañon City. No freight has been
shipped on the Tennessee Pass Line since 1997, but in relatively recent (2011)
conversations with the UP, there was no indication that UP would abandon this line in the
near future. There have been no changes since." On November 14, 2019, a CEO named Stefan Solow announced that he planned on buying the line using Colorado Pacific railway company to import and export grain from Kansas heading West to Dotsero and head en route to California, Nevada and Utah along the Moffat route after receiving a letter from a Colorado Pacific general counselor named William Osborn.
Union Pacific began actively discussing the sale of the line to Colorado pacific in 2019, for an amount of 10 million dollars. However, Colorado Pacific wanted the 8.8 million dollars that the line was valued at. After
Tennessee Pass (Colorado)