The race is held on a loop course on 4WD roads, dirt trails, and cross country in Southern Colorado's San Juan Range, US.

[1] The race has been held in early July of each year beginning in 1992, except for 1995 (too much snow), 2002 (nearby forest fires), 2019 (trail damage due to avalanche), and 2020 (global pandemic).

In order to complete the event, instead of crossing a finish line, runners are required to "kiss the Hardrock", a picture of a ram's head painted on a large block of stone mining debris.

In addition, the course covers extremely rugged terrain including steep scree climbs and descents, snow packs, river crossings, and boulder fields.

While Hardrock is nominally a running event, many entrants use equipment typically used for hiking or mountain climbing, such as trekking poles or crampons.

In 1990-1991 Gordon Hardman (Boulder and Lake City, CO), John Cappis (Telluride, CO and Los Alamos NM), and Charlie Thorn (Los Alamos, NM) began searching out other ultrarunners interested in developing a 100-mile race course through the San Juan Mountains that would include Lake City, Silverton, Telluride, and Ouray.

Roads, whether they be paved, or dirt jeep tracks, have gradually been eliminated when possible to endeavor to keep the "pure trail" nature of the event intact.

The exact lottery process has changed multiple times over the event's history, as the Run Committee is "always reviewing what we think is a fair mix and will continue to do so in the future[5]."