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Stone Mill 50 Mile



50.0 mile 80.5 kilometer point to point
97% Runnable


Ascent: 3,396' 1,035 m
Descent: -3,392' -1,034 m
High: 436' 133 m
Low: 178' 54 m


Avg Grade: 3% (1°)
Max Grade: 19% (11°)


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Trail shared by Pam Smith

50 mile trail race in Montgomery County MD

Pam Smith

Features Fall Colors · River/Creek · Views


The Stone Mill 50 Mile is a 50 mile trail run on the Seneca Greenway and Muddy Branch trails in Montgomery County Md. Traveling over rolling terrain will be a treat for those "hilly-goats" among us, and this is a challenging route.

Need to Know

The race provides drop bags at mile 25ish (Pennyfield lock) and mile 43ish (Riffleford Rd). Aid stations are well stocked, even the ones that claim to only be water stops because the volunteers are so awesome!. Aid is located at (approximately) miles: 8, 12.8, 16, 18.2, 25.1, 28.6, 35, 38, 42.8, and 48. SAG is available at any aid station. Spectators are also welcome at any Aid Station with enough parking to safely accommodate (please visit website for details).

Runner Notes

Mile 1 and 49 are on the paved path along Watkins Mill Rd between the Greenway trail and the school (start/finish line). Mile 11-13 (approximate) is on the paved path along route 28 (between the Long Draught Trail and Muddy Branch Trail). Approximately 3 miles of the course is on the C&O canal towpath (flat, crushed gravel surface)... between Pennyfield Lock AS (~mile 25) and Stone Mill AS (~ mile 28.6). Almost all of the rest is true trail/dirt surface.


The course traverses forested, rolling terrain of Montgomery County as you run towards the Potomac river on the Muddy Branch trail and then return via the Seneca Greenway trail . The course is primarily on singletrack dirt and there are small stream crossings. Most sections of the trails drain well, but lower areas can be muddy in wet weather. The course is labeled extremely well by tree blazes and/or flags on race day, which makes it difficult to get lost.

History & Background

The course will have you visit the namesake Stone Mill as you near the aid station at mile 28.6

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