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greenBlue Dirty Bismark

  3.9 ( 15 ) Favorite


15.7 mile 25.2 kilometer loop


Ascent: 970' 296 m
Descent: -970' -296 m
High: 5,960' 1,817 m
Low: 5,522' 1,683 m


Avg Grade: 2% (1°)
Max Grade: 13% (7°)


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Trail shared by Amanda Stone

A rare, long, flat-ish loop on dirt in the Front Range, named after the Morgul Bismarck road cycling route.

Amanda Stone

Features -none-

Parking fees apply at select parking lots.

Please be courteous in regards to trail closures. Large portions of this trail are clay and are therefore easily damaged while wet. Check this website for any current closures: maps.bouldercolorado.gov/os…?


The Dirty Bismark loops takes advantage of a network of dirt trails and doubletrack in the Marshall Mesa area to make a large loop. It is mostly smooth with a couple smaller technical parts.

Need to Know

Watch out for animals on the trail - cows, prairie dogs, and rattlesnakes mostly.

Some of the parking areas require Boulder County license plates or a user fee for cars registered outside of the county.

The trail can get hot and windy as there is no tree cover. Parts of the singletrack on the west side can become very muddy with rain or snow.

This is a popular MTB route with many beginners, so try to be understanding of the many users on this trail.


You can start at the Marshall Mesa Trail as shown here, but there are numerous trailheads along the loop for access. The route description is clockwise from Marshall Mesa.

Start by heading east on Marshall Valley. You'll come to the intersection with Community Ditch, but stay straight to head east on Cowdrey Draw. You'll cross a small side road where the trail turns into Mayhoffer Singletree. Keep following the obvious route. This turns into Meadowlark. At the bottom of the hill is a small parking lot with restrooms.

From here, turn right to climb up the doubletrack Coalton. Watch for cows and prairie dogs. Coalton will take a sharp left at the top of the hill and wind back toward 128 where you'll find another small parking area. From here, the trail becomes the High Plains trail with finally some nice flowing singletrack.

At the end of this singletrack section is the Greenbelt Plateau parking area. At the parking area, turn right to follow the doubletrack up the hill. At the very end of Greenbelt Plateau you'll encounter a small rock feature and intersect with
Community Ditch. Turn left onto Community Ditch until you reach the intersection for Coal Seam. Take a hard right to follow the slightly rock Coal Seam back down to the Marshall Mesa Trail.

Flora & Fauna

Rattlesnakes, prairie dogs, yucca.

History & Background

The Morgul Bismarck is a relatively famous stage from the Red Zinger / Coors Classic road cycling race from the 1970's and 1980's. Over time, trails along the perimeter of this classic road route have been built, making the Dirty Bismarck MTB trail.

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Jan 14, 2019
Meow Cat Heavy Industries
Had a great time, 8pm it got too late. Called an Lyft at Greenbelt Plateau parking lot. Trail was in good condition except parts on Coalton Trail. — 6h 00m
Jul 8, 2018
Wendy F

Trail Ratings

  3.9 from 15 votes


  3.9 from 15 votes
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