Jim rode Sagebrush to pick up Cousin Julian from the train depot on Julian's first trip to Miradero. Jim was also riding Sagebrush when he witnessed the destruction of his handcar at Dead Man's Curve.
Lucky rode Sagebrush to find Spirit during an electrical storm when Lucky was worried that Spirit might be attacked by a mountain lion. After Spirit's herd passed Lucky and Sagebrush stampeding in the opposite direction, Sagebrush became spooked by something, threw Lucky, and ran home, abandoning Lucky in the wilderness.
A sagebrush is a subshrub of the genus Artemisia. One particular species of sagebrush, Artemisia tridentata, has a bitter juice and an odor resembling sage, and covers vast tracts of alkaline plains in the western United States.