If geographic ranges are assigned to the named subspecies of deer mice that occur in Washington, it must, in part, be done arbitrarily. The deer mice of the San Juan Islands are all referred to the subspecies _hollisteri_. Only Puget Island, Wahkiakum County, is considered to be inhabitated by _rubidus_. The boundary between the ranges of _austerus_ and _oreas_ is sharply defined and further collecting by resident naturalists should result in detailed mapping of the boundary. The ranges and distribution of the deer mice of eastern Washington are less clearly defined than those of western Washington. _Peromyscus m. gambelii_ exists in its purest state on the Columbian Plateau. Here the Columbia River makes a convenient boundary to the west. Pure _Peromyscus m. oreas_ exist in the Cascade Mountains. In the area between the Columbian Plateau and the Cascades the deer mice are variously intermediate between _gambelii_ and _oreas_ and, over most of the area, are nearest to _gambelii_. This might be considered a natural area of intergradation such as commonly occurs between the ranges of subspecies. These intergrades, however, are similar to _Peromyscus m. artemisiae_ and the area occupied by these intermediates is connected on the north with the range of _artemisiae_. Thus Osgood (1909: 61) regards specimens from Easton and Wawawai, in the area of intergradation, as _artemisiae_ or intergrades between _gambelii_ and _artemisiae_. Taylor and Shaw (1929: 22) include the entire area of _intergradation_ in the range of _artemisiae_. This treatment, although convenient to the student of geographic variation, is apt to conceal the evolutionary and historical influences. These influences may be appreciated better if the intergrades from each locality are referred to the subspecies they most closely resemble.