Looking for a fun way to support trail expansion in Montana? Head to Three Forks for this event featuring 5K, 10K, and half marathon options on the scenic, mostly flat Headwaters Trail System, with all routes passing the Three Forks Ponds and Madison River Pedestrian Bridge (the half marathon also ventures through Headwaters State Park near where three major rivers converge). Registration is $35 for the shorter distances and $40 for the half marathon, and you'll get chip timing, a t-shirt, water stations throughout, and post-race refreshments—with all proceeds going toward building more trails in the area.