Some of Colorado's mountain passes can involve a pretty steep ascend to the top. It's one of the thrills of driving through the Rocky Mountains. Just how steep is Colorado's steepest road, and just how high does it go?

Get ready to climb to 11,500 feet as we take a closer look at Colorado's Highway 149 in Hinsdale County. This highway travels from the Curecanti National Recreation Area to South Fork Colorado, and includes a climb over the infamous Slumgullion Summit.

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America's 5 Steepest Highways

  • California Route 108 over the Sonora Pass includes a max grade of 26%
  • Texas 170 around Big Bend Ranch State Park includes a max grade of 15%
  • Utah Route 143 from Parowan to Panguitch includes a 13% grade around Brian Head Ski Resort.
  • Wyoming Route 14 in Shell Canyon includes a max grade of 13.5%
  • Colorado 149 over Slumgullion Summit includes a max grade of 9.5%

Colorado's Steepest Highway

Colorado 149 is also known as the Silverthread Scenic Byway. This 125-mile run through the San Juan Mountains and the Rio Grande National Forrest includes a climb up one of Colorado's oldest mountain roads. This seven-mile ascent tops out at 11,500 feet and includes a few scenic overlooks and a natural landmark. Take a closer look at Colorado's steepest highway below.

Slumgullion Earthflow

Near the top of the climb up the Slumgullion summit is the Slumgullion Earthflow overlook. Nearly 800 years ago a portion of the Mesa Soca collapsed causing an earthflow that ended up damning the Lake Fork of the Gunnison and forming Colorado's second-largest lake, Lake San Cristobal. The earthflow is still moving today at the rate of about 20 feet per year. The area is now a national landmark. Hikers and visitors can sometimes say they feel the earth move under their feet.

Colorado's steepest road is a pretty fascinating place if you can stand the climb. Take a closer look below.

10 Crazy Cool Facts About Colorado's Steepest Highway

One of Colorado's legendary scenic byways also happens to be one of the steepest highways in America. We're headed up to the Slumgullion Summit to take a look at Colorado 149 in Hinsdale County. This historic route through the San Juan Mountains features an incredible view of the Uncompahgre Peak and wilderness area.

LOOK: Colorado's Amazing Mountain Passes Ranked By Elevation

Maintain a good grip on the steering wheel because we traveling to the top of the Rockies via Colorado's extreme mountain passes. Scroll on to learn more about mountain passes above 10,000 feet throughout the state.

KEEP GOING: 15 of Colorado’s Most Extreme Mountain Roads

Some of Colorado's highest mountain roads offer incredible views, but they will also test the nerve of anyone behind the wheel. Scroll on for elevation gains, steep grades, and some amazing views while we white-knuckle our way through the Rockies.

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