The rock art of northwestern Mongolia preserves vital documentation of prehistoric life in its transition from a hunting-foraging economy to pastoralism and finally, with the adoption of horse riding, to full mounted nomadism. This pictorial record is most abundant within two long river valleys: those of Tsagaan Gol and Baga Oigor Gol. Their location in the high Altai Mountains marks the nexus between North and Central Asia, taiga and steppe, and...