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Three Creeks Half Marathon
Along three creeks through Cherry Creek State Park
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Desert RATS Trail Running Festival
Desert trails past the Colorado River and towering mesas
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Boulder Rez Half Marathon, 10K and 5K
Scenic Boulder spring race with glamorous finisher medals
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Mountain Ridge Trail Race
Front Range views along Douglas County's trail
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Platte River Half Marathon & Relay
Denvers oldest half marathon along the sunlit Platte River
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Rattler Trail Races
Technical singletrack past sandstone bluffs with Pikes Peak views
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Earth Day 5K
Durango Nature Studies' Earth Day fun run
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Horsetooth Half Marathon
Point-to-point past shimmering Horsetooth Reservoir
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Runs With Scissors Races (Half Marathon, Marathon, 50k)
Marathon, half & 50K all run on a 1.31-mile loop
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Cheyenne Mountain Trail Race
Climbs Cheyenne Mountain State Park's foothill trails
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Strut for Mutts
The furriest 5K in western Colorado
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NoCo Half Marathon & 10K
Flat lakefront course around Boyd Lake State Park
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All-Out Beat the Heat
Views of Standley Lake against the Front Range
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Royal Gorge Groove Trail Runs
Trail running along the rim of a 900-foot canyon gorge
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Bigfoot Days Half Marathon and 5K
Scenic mountain roads just outside Rocky Mountain National Park
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Unicorn 5k (Denver-East)
Unicorn-themed 5K finishing at Denver's Great Lawn Park
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Blue Heron Half Marathon
Runs through Adams County's Regional Park
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Save any of these to your season in RunCalendar and hear the morning entries open. Free on iPhone, no account needed.
Every race here is published by its organiser; RunCalendar checks the date and the entry window against the organiser's own page and rebuilds this calendar every night. A confirmed date shows its day; a provisional one shows only its month. Last updated 22 October 2026.