Colorado's Premier Fall Race Series: Registration for Boulderthon 2024 is now open! Run a 5k, 10k, Half, or Full, at the foothills of the Rockies, in the stunning running mecca of Boulder. Run the streets Olympians train on, then celebrate at our epic after-party downtown!

Boulderthon is one of the top-rated marathons in the United States: Named #5 Best Half Marathon in the US by Active, as well as #1 Best in Colorado and #13 Most Beautiful Marathon in the World by HalfMarathons.Net, Boulderthon drew over 7,000 runners from all 50 states and 18 countries in 3, nearly tripling in registration, and selling out.

Tucked into a picturesque valley below the iconic Flatirons, Boulder, Colorado sets the backdrop for the top-ranked, signature Boulder Marathon, Boulderthon. Boulder is a world-class destination offering 300 days of sunshine and endless recreation, shopping, dining, cultural and entertainment choices. It's no wonder National Geographic named Boulder the Happiest City in America.