Big 10 Curve (Denver)

Big Ten Curve sits on Union Pacific's Moffat Tunnel Subdivision at approximately milepost 20-21, where the single-track main line wraps 270 degrees around a small mesa to gain elevation on the climb from the Denver suburbs into the Front Range foothills. The best public vantage point is from Blue Mountain Road, which crosses the tracks at grade just west of Eisele siding and provides an elevated overlook above the curve. From here, you can watch westbound trains approach from Rocky siding, negotiate the sweeping S-curve through Little Ten and Big Ten, and continue climbing toward Tunnel 1 and the tunnel district beyond.

Train speeds are slow through this section — the constant 2% grade means freights are working hard uphill and using dynamic brakes downhill. UP issues 10 mph slow orders through Big Ten during high-wind events. The passing sidings at Rocky (MP 17.4-19.0, 7,330 ft long) and Eisele (MP 20.6-21.8, 5,780 ft long) are both visible from the overlook area, so meets between opposing trains occasionally play out in full view. Radio scanners tuned to 160.455 MHz (the frequency from East Rocky westward) let you follow crew-dispatcher communication in real time.

A Virtual Railfan webcam is positioned on the hillside near MP 21.3, offering a live feed of the curve available to subscribers on the Virtual Railfan website. The camera has pan-tilt-zoom capability operated by moderators.

Big Ten Curve occupies the transition zone where the Colorado Great Plains meet the Front Range foothills, at roughly 7,000-7,200 feet elevation. To the east, the terrain opens into rolling grassland with views of the Denver skyline approximately 15 miles away. To the west and south, red sandstone hogbacks and pine-dotted slopes mark the beginning of the mountain climb. The curve itself wraps around a low mesa just south of the former Rocky Flats nuclear weapons site (now the Rocky Flats National Wildlife Refuge).

The signature visual element is the row of roughly two dozen hopper cars permanently parked on a siding inside the curve — filled with cement and dirt, welded to the rails, and painted an earthy tone to blend with the terrain. This windbreak, installed by the Denver & Rio Grande Western between late 1971 and early 1973, stands as a striking and photogenic reminder of the extreme wind conditions here. Chinook winds sweeping off the Continental Divide can exceed 70-90 mph at this exposed location, and on at least two occasions before the windbreak was installed, trains were literally blown off the tracks. The surrounding vegetation is high-plains scrub typical of the Colorado Piedmont at this elevation.

As of mid-2023, the Moffat Tunnel Subdivision through Big Ten Curve averages about six train movements per 24-hour period. The daily fixtures are Amtrak's California Zephyr: Train #5 westbound passes around 8:45 AM and Train #6 eastbound around 5:30 PM when on schedule. BNSF operates a nearly daily manifest in each direction between Denver and Provo, Utah (symbols HDENPVO and HPVODEN), running under trackage rights over UP. Union Pacific runs its own manifest between Denver and Grand Junction (MNYGJ/MGJNY) roughly three times per week, though these often move in darkness.

Seasonal passenger extras include the Rocky Mountaineer (April through October, running westbound Sunday/Wednesday around 9:40 AM, eastbound Tuesday/Friday around 5:00 PM) and Amtrak's Winter Park Express ski train (Friday through Sunday, January through March, westbound around 7:45 AM, eastbound around 5:30 PM). Random unit trains — oil, frac sand, and coal — add sporadic extra movements. UP's West Local serves an aggregate plant on the Rocky Flats Industrial Lead spur roughly every third Wednesday.

The classic elevated shot is from the hillside above Blue Mountain Road, where the full arc of Big Ten Curve fits into a wide-angle frame (24-35 mm range). From this vantage, you can capture trains wrapping the curve with the hopper-car windbreak visible inside the arc and the Denver skyline on the horizon. Morning light illuminates eastbound trains head-on against the city backdrop; afternoon light creates dramatic sidelit compositions on westbound climbers.

For telephoto work (100-400 mm), the Blue Mountain Road grade crossing itself offers close-up angles on trains entering and exiting the curve, with the hopper cars providing a unique foreground element. A hiking trail on the adjacent ridge — the same trail used by photographer Mike Danneman and historically by Ralph Parsons for Robert LaMassena's book "Colorado's Mountain Railroads" — provides an overhead perspective looking down on Tunnel 1's east portal. From there, late afternoon and sunset light paints the sandstone and locomotive exhaust in warm tones.

Note that Tunnel 1, at 366 feet long, has a quirk: the west portal is actually geographically east of the east portal due to the extreme curvature, making for unusual compositions as trains emerge heading north after entering heading east.

Construction of the line began in December 1902 under David H. Moffat's Denver, Northwestern & Pacific Railway (DNW&P), with Chief Engineer H.A. Sumner facing the challenge of gaining over 4,000 feet of elevation in 50 miles while keeping grades at or below 2%. The direct route between Rocky and Coal Creek Canyon needed to rise roughly 300-350 feet across only 3,300 feet of horizontal distance — an impossible 9% grade for a railroad. Sumner's solution was Big Ten Curve: by stretching the route to approximately 3 miles (16,500 feet of track) through a series of 10-degree curves, he reduced the average grade to 1.8%.

The DNW&P was reorganized as the Denver & Salt Lake Railway in 1913 after Moffat's death in 1911. The D&SL was acquired by the Denver & Rio Grande Western in 1931, which built the Dotsero Cutoff in 1934 to finally connect Denver directly with Salt Lake City via the 6.2-mile Moffat Tunnel (completed 1927). The D&RGW was absorbed by Southern Pacific in 1988 and subsequently by Union Pacific in 1996.

The hopper-car windbreak was installed between December 1971 and early 1973 by the D&RGW after repeated wind-related derailments — including a November 1971 incident where high winds blew auto rack cars off the tracks at Big Ten. About two dozen hoppers with old-style journal boxes were filled with cement and dirt, dragged onto a purpose-built siding track, welded in place, and painted to blend with the terrain. They remain in place today, one of the most recognizable and photographed features on any American railroad.

Big Ten Curve is one of the most accessible mountain railroading locations in the American West — roughly 30 minutes from downtown Denver by car, yet offering the full spectacle of trains fighting a 2% grade through 270 degrees of curvature at the foot of the Rocky Mountains. The hopper-car windbreak is a feature found nowhere else on a North American railroad: a permanent train-on-a-track serving as infrastructure rather than rolling stock. The curve's geometry means that from a single elevated vantage point, you can see a long train simultaneously head-on, broadside, and tail-end without moving. Six miles of track connect two points only 1.5 miles apart horizontally but displaced 600 feet vertically — a statistic that captures the engineering audacity of David Moffat's railroad.