A second group includes species with close relatives in both the Rocky Mountain and Pacific Coastal faunas. This group is remarkable in that it is composed of either very closely related species or very strongly differentiated subspecies in each fauna. For example, the golden-mantled ground squirrel (_Citellus saturatus_) of the Cascade Mountains is specifically distinct from _Citellus lateralis_. Supposedly the Cascade form was isolated in the southern Cascades during Vashon-Wisconsin time. The Douglas squirrel (_Tamiasciurus douglasii_) of the Cascades, which has a red belly, is the same as the squirrel of the lowlands of western Washington but is specifically distinct from the red squirrel (_Tamiasciurus hudsonicus_) of the Rocky Mountain Fauna, which has a white belly. In the extreme northeastern Cascades the two species come together. They do not interbreed but seem to compete, for they do not occur together. The flying squirrel (_Glaucomys sabrinus fuliginosus_) of the Cascades is only slightly differentiated from other races of the Rocky Mountain Fauna but is much different, as are all Rocky Mountain races, from the western Washington subspecies (_Glaucomys s. oregonensis_). The red-backed mouse of the Cascades is _Clethrionomys gapperi_, a species distinct from _Clethrionomys californicus_ of western Washington. The jumping mouse of the Cascades is _Zapus princeps trinotatus_, the same race that occurs in western Washington. It is quite distinct from, and has previously been considered a species separate from, the races of the Rocky Mountain Fauna. The snowshoe rabbit of the Cascades is closely related to other races of the Rocky Mountain Fauna but is distinct from _L. a. washingtonii_ of western Washington. The pika (_Ochotona princeps_) of the Cascades was apparently isolated in the southern part of the range during the glaciation. After the retreat of the glaciers it extended its range northward. Competition between two subspecies has resulted in parallel distributions due to relative body size. The two races freely intergrade and the differences between them are not so great as in the other forms mentioned. The third group of mammalian species of the Cascades is composed of species typical of the Rocky Mountain Fauna such as: _Marmota caligata_, _Synaptomys borealis_, and _Orcamnos americanus_. Each has no ecological counterpart in the Pacific Coastal Fauna. Each is absent from the Cascades of Oregon.