Near the end of the last Ice Age, America’s first people migrated into the lake-filled Fort Rock basin, where the climate was cooler than today’s. As warming increased evaporation and the lake shrank, they found caves carved by waves from times when lake levels were higher. Around 9000 years ago, sagebrush adapted to arid conditions replaced much of the marsh grasses, yet human habitation in the caves is thought to have continued for more than 11,000 years despite the shift from temperate to semiarid conditions. Bones found in the caves indicate that game remained plentiful, and charcoal from fire pits traces the gradual disappearance of plant types no longer found there. More than 70 sandals woven from sagebrush bark have been found in caves across the basin, along with mats and baskets made from the same material. Stone arrowheads and spear points, scrapers, gravers, and fish net weights found throughout the basin reflect a resident population with many food sources.