One circular trapline of 159.5 feet radius was established in November 1961, and was tended for 30 consecutive days to observe the effect of removing the more dominant species (Calhoun, 1959).
Other mouse traps and rat traps were set in suitable places on talus slopes, rocky cliffs, and in cliff dwellings. Most of these traps were operated for three consecutive nights.
In order to test hypotheses concerning habitat preferences of each of the species of _Peromyscus_, several previously untrapped areas that appeared to be ideal habitat for one species, but not for the other, were selected for sampling. In the summers of 1963 and 1964 snap traps were set along an arbitrary line through each of these areas. Traps were placed in pairs; each pair was 20 feet from the adjacent pairs.
A mixture of equal parts of peanut butter, bacon grease, raisins, roman meal and rolled oats was used as bait. Rolled oats or coarsely ground scratch feed was used in areas where insects removed the mixture from the traps.
Rodents trapped by me were variously prepared as study skins with skulls, as flat skins with skulls, as skeletons, as skulls only, or as alcoholics. Representative specimens were deposited in The University of Kansas Museum of Natural History. In the course of my study, traps were set in the following areas:
In July 1959 a fire destroyed more than 2,000 acres of pinyon-juniper forest (_Pinus edulis_ and _Juniperus osteosperma_) in the eastern part of the park. The burned area extends from Morfield Canyon to Waters Canyon, encompassing several canyons, Whites Mesa, and a ridge between Morfield Canyon and Waters Canyon that is known locally as Morfield Ridge (Fig. 1). Beginning on September 4, 1961, three pairs of traplines were run on this ridge at elevations of 7,300 to 7,600 feet.
Vegetation in the trapping area consisted of dense growths of grasses and herbaceous plants, which had covered the ground with seeds. In this and in the following accounts, the generic and specific names of plants are those used by Welsh and Erdman (1964). The following plants were identified from the trapping area on Morfield Ridge:
_Lithospermum ruderale_ _Chenopodium pratericola_ _Achillea millefolium_ _Artemisia tridentata_ _Aster bigelovii_ _Chrysothamnus depressus_ _Chrysothamnus nauseosus_ _Helianthus annuus_ _Helianthella_ sp. _Lactuca_ sp. _Lepidium montanum_ _Quercus gambelii_ _Agropyron smithii_ _Bromus inermis_ _Bromus japonicus_ _Oryzopsis hymenoides_ _Calochortus nuttallii_ _Linum perenne_ _Sphaeralcea coccinea_ _Polygonum sawatchense_ _Solidago petradoria_ _Wyethia arizonica_ _Nicotiana attenuata_ _Fendlera rupicola_ _Penstemon linarioides_