O'Brien Trail Races

O'Brien Trail Races take place in Marine on St. Croix, Minnesota, on September 26, 2026. The event offers four trail distances with closely spaced starts: a 50K (31 miles) at 8:00 a.m., a 25K (about 15.5 miles) at 9:00 a.m., a 10K at 9:05 a.m., and a 5K at 9:10 a.m. All are run on trails near the St. Croix River in eastern Minnesota, which makes it easy for a group with mixed abilities to race the same morning.

Beginners and families will find the 5K and 10K approachable, while the 25K is a good fit for runners stepping up from a road half marathon. The 50K works well as a first ultra thanks to the comparatively late start. For the 25K, plan 10 to 12 weeks with a weekly long trail run and some hill sessions; for the 50K, extend that to 16 weeks and add back-to-back long runs, plus practice eating on the move. Trail shoes with decent grip will help on any of the four distances.