Establishing the ancestral area of a taxon is a central theme of historical biogeography. We used the cladistic method of ancestral area analysis devised in 1992 by K. Bremer to determine the ancestral area of rattlesnakes (genera Crotalus and Sistrurus). We then extended this approach to determine the vegetation type of the ancestral area. The most probable ancestral area of rattlesnakes is the Madrean Occidental. The most probable vegetation of the ancestral area was pine-oak forest. Knowledge of the ancestral area and its vegetation was applied to macroevolutionary hypotheses regarding the evolution of the rattlesnake rattle.