100K October ultramarathons in United States

10-mile loop on Blue Wing, Koasati, and Whoa Mule trails with flat, muddy paths, tree roots, and views of Lake Bistineau and cypress forests

Rocky ascents and descents along shaded and open trails with lake views at Dana Peak Park; single-loop courses with minimal trail repetition.

Three-loop course through Cuyamaca Rancho State Park, summiting Cuyamaca Peak, circling Oakzanita Peak, and running PCT segments with desert views.

Diverse and challenging dirt and single-track trails, panoramic vistas, moderate elevation gain of 1,930 ft (50km) and 4,250 ft (100km)

Flat course through St. Croix State Park, forest and prairie trails, Kettle River views, historic fire tower climb, generous cutoff times

Challenging 100k along Pennsylvania's Black Forest Trail with over 13,400 ft of climbing, midnight start, rugged forests, and shifting toughest sections

Remote gravel roads through Flint Hills prairie, open rangeland, rolling hills, 6,000 feet of climbing, scenic out-and-back and loop sections near Eureka and T.

Mountain routes near Los Angeles featuring Big Bear Lake views, Sugarloaf Mountain ascents, and descents into Siberia Canyon

10.48-mile pine barrens trail loop in Rocky Point, with ultramarathon distances from 50K to 150 miles and flexible start times

Scenic loop course through Ponderosa State Park, featuring accessible trail terrain and a community-focused atmosphere

Rugged single-track ultramarathons on the Gerard Hiking Trail, with over 17,000 feet of elevation gain through Oil Creek State Park's scenic, demanding terrain

Point-to-point and out-and-back ultramarathon across Michigan’s lower peninsula, with varied single-track, gravel, limestone, and seasonal road terrain

Varied single track and jeep paths through old growth woods, lakes, and rolling hills on a 1,000-acre private ranch, with gravel, dirt, sand, and roots

Scenic trail loops at High Hope Ranch and Eco-Retreat, combining 3.3- and 7-mile sections for a 10.3-mile lap with moderate difficulty and spaced aid stations.

Scenic Hill Country ranch terrain on well-marked 10.5-mile loops with spaced aid stations, challenging 100K and 50K distances, camping available

Grassy paths, dirt single track, creek crossing, and demanding hills on private land between Fox Ridge State Park and Warbler Ridge in Charleston, IL

Steep climbs, technical paths, and flat prairie trails on a looped course through forests and bluffs, featuring river views in Iowa's driftless region.

Rugged gravel and prairie course through Cookson Hills’ oak-hickory forests and valleys, with fall foliage and Illinois River views in the J.T. Nickel Preserve

Rugged Superior Hiking Trail paths, challenging 50K and 100K routes, rocky and root-covered terrain, sweeping Duluth and Lake Superior views