100mi May ultramarathons in United States

Rugged 100-mile course on ATV trails and forest paths in Androscoggin Riverlands State Park, with technical sections, river views, and constant undulations.

Demanding 20-mile loop on rugged singletrack, nearly all trail with two road crossings and about 2,700 feet of elevation gain per loop.

100 miles across the Black Mountains with five major climbs, technical trails, and over 21,500 ft of elevation change from Camp Grier to Mt. Mitchell

Standard outdoor track ultramarathon with minimal on-course support and a focus on community and mental health awareness

Fast 20-mile dirt loops on singletrack and double track, with rolling hills, 2,300 ft of climbing per loop, and a mild coastal spring setting.

Technical 100-mile course across rocky trails and steep climbs in Virginia's Massanutten Mountains, with over 18,000 feet of elevation gain

100-mile point-to-point route from Key Largo to Key West, ocean-side course, individual and team divisions, scenic views along the Florida Keys

3.0-mile loop with 237 feet of elevation gain per lap, mostly shaded gravel camp roads and trails, late May temperatures between 58 and 78 degrees

Track-based 100-mile relay featuring team participation, a festive atmosphere, live progress updates, and community-focused support against hunger

Silver Towers, Ripton, Vermont, with routes into the Green Mountain National Forest and ultra distances extending to 551 miles.

Full-moon trail weekend with evening starts, steep sustained climbs, high-elevation terrain to 6,200 feet, and rugged mountain-style efforts.

Flat 1-mile dirt and grass loops on a private horse ranch in Riverside, lap-based ultra with accessible support and camping options for families and crews

6- or 12-hour timed challenge on a 5K mixed trail and road loop with community support, crew tents, amenities, and celebratory atmosphere in the park

Singletrack loop course at 7,200 ft in New Mexico's national forest, technical sections, elevation changes, solar-lit night running, free camping, no mid-race 


Looped course on scenic trails at Calvin Crest with marathon, 100-mile, and 13-hour options; cumulative elevation gains and strict Sunday cutoff

Continuous 4-mile trail loop through varied park landscapes with nighttime sections, aid stations, camping, and wildlife along the route

Rolling loop course at Lake Youngs Watershed with 900 feet of elevation gain per lap and a well-supported, community atmosphere

24-hour backyard ultra with repeated hourly loops, shared aid hub, and a last-runner-standing format shaped by pacing, recovery, and endurance.

Rolling jeep trails and river views along the Chesterfield Gorge, featuring out-and-backs on unpaved terrain with permanent mile markers