Tartarus Backyard Ultra is a last-person-standing race held at Camp 7 in Riverside State Park, Spokane, Washington, featuring distinct competitions for runners and ruckers. Each lap begins on the hour. Participants are eliminated if they miss the time limit, start late, or are not in the corral before the bell. Runners complete 4.1667 miles per lap. Ruckers cover 2.2 miles, carrying a pack weighing 30 pounds for those over 150 pounds body weight, and 20 pounds for those under.
The race continues until only one runner and one rucker remain to complete a final solo lap. The daytime course follows looped trails within the park. At night, it shifts to an out-and-back route on the Centennial Trail before returning to the park loops the following morning. Racers provide their own aid, though crews may offer support. The start-finish area provides each participant a small space for a chair and equipment. The ruck division requires traditional rucks only, prohibiting vests, establishing it as a unique challenge rather than a simplified version of the running race.