Big 10 Curve (Denver) – Arvada, Colorado, USA | Train Spotting Location

From the public pull-offs along Colorado State Highway 93 or the adjacent county road network, railfans gain unobstructed sightlines both eastbound and westbound. Southbound (geographically compass-west) trains approach slowly from Rocky Flats, nose into the 10-degree curve, and then disappear toward Tunnel 1; northbound consists emerge silently from the tunnel portal before throttling up for the descent to Clay. Because of the grade, most freights pass at 20–25 mph, giving ample time to identify locomotives, distributed power units, and car types. Expect the ground to vibrate and turbochargers to whistle as multiple GEVOs or SD70ACe helpers dig in. Even a standard manifest can run 6,000–8,000 feet, and coal drags often exceed 100 cars, so the sight of a train occupying the whole arc is common. Ambient highway noise is low, and the nearest community is several miles away, letting rail sounds dominate the scene.

Big 10 Curve sits at roughly 7,100 feet above sea level on the eastern face of the Front Range. To the east stretch the open grasslands of the Colorado Piedmont; to the west rise red sandstone hogbacks and pine-dotted slopes. The curve itself is carved into a south-facing hillside, giving visitors wide vistas of the foothills and, on clear days, downtown Denver 15 miles distant. Vegetation is high-plains scrub: rabbitbrush, yucca, and scattered juniper. Summer afternoons bring dry heat, golden light, and sudden thunderheads that can yield dramatic photo backdrops. Winter visits require warm layers; chinook winds can exceed 40 mph, and snow squalls sweep off the Continental Divide, dusting the right-of-way in minutes.

The line is Union Pacific’s Moffat Route, a critical trans-Rocky Mountains artery. On an average weekday, railfans can expect 12–18 freight movements, a mix of:
• Unit coal trains from the North Fork Valley
• Manifest freights serving Utah and Pacific Northwest gateways
• Occasional intermodal or autorack extras
• Maintenance or geometry trains several times per month
Amtrak’s California Zephyr adds one passenger movement in each direction daily, usually mid-morning westbound and late afternoon eastbound. Power is predominantly UP AC4400CW, ES44AC, and SD70ACe, with BNSF run-through units appearing on coal sets. Distributed power on the rear or in-train is routine to counter the climb to the 6.2-mile Moffat Tunnel.

The classic photo is taken from the dirt access road on the hillside above the tracks—here the entire “S” curve fits into a 24-mm frame, with trains wrapping 270 degrees around the photographer’s vantage. Morning light favors eastbound shots, illuminating the train’s nose and the Denver skyline in the distance; afternoons backlight locomotive exhaust and highlight dust kicked up by dynamic brakes. Telephoto lenses (100–400 mm) capture the locomotives emerging beneath the wind-screen of retired hopper cars that line the outside of the curve—a unique detail no other spot offers. A second angle, reachable by a short hike up the adjacent ridge, looks down on Tunnel 1’s east portal; from there, sunset light paints locomotives and sandstone in warm tones.

Completed in 1904 as part of David Moffat’s Denver, Northwestern & Pacific Railway, the curve was engineered to tame the steep climb out of the plains toward the Continental Divide. Its name comes from the tight 10-degree curvature—a remarkable figure for a mountain main line designed for heavy, long trains. In the 1970s, the Rio Grande welded 33 surplus hopper cars together, filled them with concrete and rock, and installed them along the outer rail to act as a wind barrier; this improvised screen still stands, a favorite photographic touchstone and a living reminder of Rio Grande ingenuity. The site also played a minor role in Cold War history: nearby Rocky Flats produced nuclear components, and special security trains once used the line.

Unlike many mountain railfan sites that require strenuous hikes or remote travel, Big 10 Curve offers front-row mountain railroading within 30 minutes of downtown Denver. The combination of slow, hard-working trains, sweeping curvature, and a built-in historical wind-screen of hopper cars creates visuals unmatched elsewhere on the Moffat Route. Few locations let observers see a full mile-long train simultaneously head-on, broadside, and tail-on without changing position.