RMRR Spring Marathon Training Series

Prepare for your spring marathon goals at the RMRR Spring Marathon Training Series, hitting the scenic Platte River Trail in Thornton, CO, on March 29, 2026. This popular event offers a perfectly timed opportunity to test your limits with both 10-mile and 20-mile distances, catering to runners fine-tuning their pace and nutrition strategies for upcoming marathons like Boston or Colfax.

The course itself features a straightforward out-n-back design along the paved Platte River Trail, guiding runners south for 5 miles before a turnaround. Those tackling the 10-mile distance will finish upon their return to the start, while 20-mile participants will repeat the course, all under the guidance of clearly marked mile markers. Typical race day conditions in late March bring pleasant spring weather, with highs around 64°F and lows around 33°F, accompanied by a low 6% chance of precipitation, creating ideal running temperatures.

As part of the Rocky Mountain Road Runners' esteemed Marathon Training Series, this low-cost, low-keyed event is renowned for its friendly, fully supported atmosphere, making it accessible to runners of all abilities. Aid stations are well-stocked with water, sports drinks, and gels to keep you fueled, and awards include ribbons and running store gift certificates for top finishers. Starting promptly at 8 AM from the Platte River Trailhead Park at 88th and Colorado, with ample parking available, the RMRR Spring Marathon Training Series is an essential tune-up for your big race.