A grassy meadow lies just to the east of the highway into the park, one-quarter of a mile southeast of the park's entrance. On July 30, 1963, one hundred traps were placed in two lines through the meadow, and were run for one night. Only individuals of _P. maniculatus_ were caught (Table 1). _M-2 Weather Station, Chapin Mesa_ The M-2 weather station of the Wetherill Mesa Archeological Project was on the middle of Chapin Mesa at an elevation of 7,200 feet. This site was in an old C. C. C. area, about one mile north of the park's U. S. Weather Bureau station. The vegetation surrounding the M-2 site was a pinyon-juniper-muttongrass association. It was thought that both species of _Peromyscus_ would occur in this habitat. On May 10, 1964, 25 traps were placed in this area and were run for one night. Only individuals of _P. truei_ were caught (Table 1). _Grassy Meadow, Southern End Moccasin Mesa_ This large meadow is located eight miles south of the northern rim of Moccasin Mesa. The meadow lies in a broad, shallow depression that forms the head of a large drainage (Fig. 1). To the south of the meadow the drainage deepens, then reaches bedrock as it approaches the pour-off. On August 23, 1964, one hundred traps were set in pairs in a line through the middle of the meadow; adjacent pairs were 20 feet from each other. Only individuals of _P. maniculatus_ were caught (Table 1). Grasses are dominant in the ground cover, and _Sphaeralcea coccinea_ (globe mallow) is codominant. The abundance of globe mallow is due to the present and past disturbance of this meadow by a colony of pocket gophers. Trees are absent in the meadow. Species of plants include the following: _Opuntia polyacantha_ _Chenopodium_ sp. _Artemisia ludoviciana_ _Chrysothamnus nauseosus_ _Koeleria cristata_ _Poa pratensis_ _Lupinus ammophilus_ _Calochortus gunnisonii_ _Erigeron speciosus_ _Gutierrezia sarothrae_ _Tetradymia canescens_ _Tragopogon pratensis_ _Bromus tectorum_ _Sphaeralcea coccinea_ _Eriogonum racemosum_ _Polygonum sawatchense_ _Comandra umbellata_ _Penstemon strictus_ _Bedrock Outcroppings, Southern End Moccasin Mesa_ Two miles south of the preceding site, much of the mesa is a wide expanse of exposed bedrock, which extends approximately 100 feet inward from the edges of the mesa. Pinyon-juniper-mixed shrub woodland adjoins the bedrock. On August 23, 1964, 25 traps were placed along the bedrock, near the edge of the forest. Only two mice, both _P. truei_, were caught. (Table 1). HOME RANGE In order to learn how extensively mice of different ages travel within their habitats, whether their home ranges overlap, and how many animals live within an area, it was necessary to determine home ranges for as many mice, of each species, as possible (Hayne, 1949; Mohr and Stumpf, 1966; Sanderson, 1966).