Plethodon cinereus occurs throughout Michigan in suitable forest, forming small isolated remnants of a population that was once largely continuous. In extreme southern Michigan the black color phase forms a large proportion of the population; in the northern tip of the Lower Peninsula less than 10 per cent of the salamanders are black; on the Upper Peninsula the black phase is apparently confined to a small area at the Straits of Mackinac. It is probably that the black phase is evolutionarily younger than the red-striped one and so has not had time to reach the limits of the species range. It probably entered Michigan long after the striped phase and only recently (perhaps 200-2,000 years ago) crossed the Straits of Mackinac. It has also reached at least one island in the straits.