This is the Union Pacific Moffat Tunnel Subdivision overlooking the Big 10 Curve near Milepost 21. The Big 10 Curve was built by the Denver, Northwestern and Pacific Railway in 1902.
The DN&P later became the Denver & Salt Lake Railroad The D&SL was acquired by the Denver & Rio Grande Western RR in 1931 (the merger was completed in March 1947).
The Big 10 curve is an S-shaped curve that traverses the transition from the Great Plains to the Front Range of the Rocky Mountains. The ‘Big Ten’ consists of “Big Ten Loop” and “Little Ten Loop”, both of which are so-named due to having curves of 10º radius. Big Ten was constructed to allow for a grade not exceeding 2%, as the line needed to gain 600 feet in elevation in 2.85 miles at a grade of 4%, which, with Big Ten, became 7 miles at 2% instead.

While the tracks here see only 10-12 trains per day on average there is no denying the beauty of this view!

The Amtrak California Zephyr (5/6) passes once per day in each direction. The Rocky Mountaineer (Rockies to the Red Rocks) passes Westbound on Tuesdays and Saturdays, and Eastbound on Mondays and Thursdays.

There is an ATCS layout for this area with partial coverage – UP Moffat Tunnel Sub East

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