The Spirit Cave Mummy from Nevada — an adult male dated to approximately 10,600 calibrated years — is geographically the closest well-known ancient individual to the Hourglass Cave man, though still separated by a substantial geographic distance and a significant age difference.

The Spirit Cave individual, whose genome was published in 2018 after a long legal dispute over repatriation, was found to be most closely related to Native American populations and carried mitochondrial haplogroup X — yet another of the five founding lineages, demonstrating the geographic spread of founder haplogroup diversity across the American West in the late Pleistocene and early Holocene.

The Kennewick Man from Washington State — dated to approximately 8,500 calibrated years and the subject of a decade-long legal dispute over scientific study versus repatriation — provided another early Holocene genetic data point from the Pacific Northwest.

His mitochondrial haplogroup was within haplogroup X, like the Spirit Cave Mummy, and his nuclear genome was found to be most closely related to modern Native Americans, particularly to the Columbia Plateau tribes that had claimed him.