Vail Passes: Environmental impact apparent on Fremont Pass |

Vail Passes: Environmental impact apparent on Fremont Pass

Rick SpitzerVail, CO Colorado
Special to the Vail Daily/Rick SpitzerLooking south from the summit of Fremont Pass.

Human impact is starkly evident on the summit of Fremont Pass, located about 11 miles southwest of Frisco on CO 91. Since the late 1870s, miners have worked the area. The Climax Molybdenum Mine located here was once the world’s leading producer of molybdenum, accounting for 75 percent of the world’s supply. Travelers going over the pass cannot miss how this level of mining activity dramatically changed the scenery here. Below the pass, in the Tenmile Valley, you can see the waste from 400 million tons of molybdenite ore that have been mined from this area. About 99 percent of the mined material is not used, and it now fills three huge tailings ponds.Even though the summit of Fremont Pass sits at 11,318 feet – making it the eighth highest pass in Colorado – the approaches from either side are among the most gentle of any pass in the state. The pass sits on the Continental Divide and divides the watershed of the Blue River on the west and the Arkansas River to the east. At one time, the Denver, South Park and Pacific Railroad and the Colorado and Southern Railway lines crossed Freemont Pass. The remains of their grades can be seen on both approaches to the summit. Today, a railroad tourist line, the Leadville, Colorado & Southern Railroad, originates in Leadville and follows the grade of the defunct railroads to a point near Fremont Pass.

In 1879. Charles Senter staked a gold ore claim on Bartlett Mountain on Fremont Pass. The ore turned out to be molybdenum, and the Climax Molybdenum Company soon formed to mine the metal, which at the time was used in lightbulb filaments.Molybdenum is an element with a very high melting point, and when added to steel it acts as a hardening agent. World War II increased the demand for this high-strength steel, and a molybdenum enhanced alloy is still used today. Molybdenum is also heat resistant and corrosion-resistant, so is often used in aircraft and missiles. It also has uses in petroleum products, lubricants and electronic parts.While the mine was in operation, it employed thousands of people, many of whom lived on site in the town of Climax. Employee housing, a school, and a hospital were once located there. Many of these buildings were later moved to Leadville and are still in use in that town. The Climax Molybdenum Company also developed the Chalk Mountain ski area west of Red Mountain Pass,. It installed a rope tow to service the 1,500-foot slope, and lined the slopes with floodlights, creating Colorado’s first night skiing facility.

Today, the open pit mine on Ceresco Ridge – a dominant feature on Fremont Pass – and the appearance of the mine buildings give the impression that the mine still operates. The mine is not currently operational, however, though there are a handful of full-time employees who care for the facility in the event that it were to reopen. Others work on the environmental reclamation of the area, including restoration of the land, and on water treatment. The pass averages 23 feet of snow each year, and three major rivers originate near it: the Arkansas, the Eagle, and Tenmile Creek.Many towns rely upon these rivers as a water source, and therefore hold great concern about the water’s quality and the treatment it receives. The Climax Molybdenum Company treats the water that comes in contact with the tailings ponds, and wastewater-treatment districts in the area are helping to recover the ponds. The municipal wastewater plants truck their sludge to the Climax ponds, where it is mixed with wood chips and other bio-solids to create topsoil. Trees and other vegetation are being planted on the site, but at 11,000 feet, where the growing season is only 10 weeks, reclamation is a very difficult process.A major wayside exhibit is planned for the summit of the pass as a feature of the Top of the Rockies Scenic and Historic Byway. The plan includes interpretive panels to explain the mining activity of the area and a display of mining artifacts.E-mail comments about this article to or visit

Rick Spitzer is the author of “Colorado Mountain Passes: the States Most Accessible High Country Roadways,” which is for sale at The Bookworm of Edwards for $21.95. Parts of the book will be serialized in the Vail Daily every Sunday this summer.

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