Pinyon mice were abundant in a variety of associations within the pinyon-juniper woodland. The highest population densities were in pinyon-juniper woodland having an understory of mixed shrubs. In such an association, _Poa fendleriana_ usually is the dominant grass in the ground cover. _P. truei_ was especially abundant along brushy slopes where mixed shrubs (_Amelanchier_, _Cercocarpos_ and _Fendlera_) were codominant with pinyon pines and Utah junipers. The pinyon-juniper-mixed shrub area west of Far View Ruins was almost optimum habitat for _P. truei_. _P. truei_ was abundant on the rocky ridge of Wetherill Mesa near Mug House; the pinyon-juniper woodland here has a _Cercocarpos_ understory, and appears to provide close to optimum conditions for this species. Not all associations of the pinyon-juniper woodland support large numbers of _P. truei_. Pinyon-juniper woodland having a ground cover of _Poa fendleriana_, and no shrubs, supports few mice; the woodland on Wetherill Mesa near Long House is an example. Juniper-pinyon woodland having a _Purshia tridentata_ understory also supports only a few mice. Such areas occur on the southern ends of the mesas and are characterized by widely-spaced trees and little ground cover--a reflection of the relatively low amounts of precipitation received by the southern end of the park. _P. truei_ was not found in grasslands on Navajo Hill, or in meadows at the southern end of Moccasin Mesa. The old burned areas on the northern end of Wetherill Mesa and on Morfield Ridge now support numerous grasses and shrubs, but _P. truei_ appears not to live there. _P. truei_ tends to avoid stands of sagebrush, or grasslands, lacking pinyon or juniper trees. _P. truei_ may venture into such areas while feeding. This species is found in thickets of Gambel oak and in areas with an overstory of mixed shrubs only when a living pinyon-juniper canopy is present, or when a woodland adjoins these areas. Rocky terrain apparently is not a requirement for _P. truei_, since much of the pinyon-juniper woodland that is free of rocks supports large numbers. Optimum habitat, however, had a rocky floor. In such places, rocks probably are of secondary importance, whereas the shrubs and other plants growing on rocky soils are important for food and cover. Rocks likely provide additional nesting sites, and allow a larger population to live in an area than might otherwise be possible. In Mesa Verde the deer mouse, _P. maniculatus_, prefers open areas having dense stands of grasses, or brushy areas adjoining open terrain. This species lives in stands of big sagebrush; in grassy areas having an oak-chaparral or mixed-shrub-overstory; and in grasslands without shrubs, such as on the southern end of Moccasin Mesa. Pure stands of sagebrush did not support large numbers of mice unless there was additional cover nearby in the form of shrubs or oak brush.