Part 2 (1/2)

Bobcat Canyon, a large secondary canyon on the eastern side of Wetherill Mesa, is a major drainage for much of the mesa at its widest part. The mesa top drains southeast into a pour-off at the head of Bobcat Canyon.

A stand of big sagebrush, _Artemisia tridentata_, grows in the sandy soil of the drainage, and extends northwest for several hundred yards from the pour-off. The sagebrush invades the pinyon-juniper forest at the periphery of the area.

Two traplines were set in the drainage, with trapping stations at intervals of 25 feet. The lines traversed elevations of 7,000 to 7,100 feet, and were run from June 26 to 29, 1962.

Gra.s.ses are the most abundant plants in the ground cover. _Artemisia dracunculus_ is common in the drainage, and _A. nova_ grows around the periphery of the drainage. Other species occurring in this stand include:

_Aster bigelovii_ _Tetradymia canescens_ _Tragopogon pratensis_ _Bromus tectorum_ _Poa fendleriana_ _Sitanion hystrix_ _Stipa comata_ _Lupinus argenteus_ _Calochortus gunnisonii_ _Sphaeralcea coccinea_ _Phlox hoodii_ _Eriogonum umbellatum_ _Peraphyllum ramosissimum_ _Purs.h.i.+a tridentata_ _Penstemon linarioides_

No mice were caught in three nights of trapping (360 trap nights), and only one mammal, a _Spermophilus variegatus_, was seen.

_North of Long House, Wetherill Mesa_

Pinyon-juniper forest with a dominant ground cover of _Poa fendleriana_ was described by Erdman (1962) as one of the three distinct types of pinyon-juniper woodland on Wetherill Mesa. Such a woodland occurs adjacent to the Bobcat Canyon drainage, and is continuous across the Mesa from above Long House to the area near Step House. Plants in the ground cover include:

_Cryptantha bakeri_ _Opuntia rhodantha_ _Chrysothamnus depressus_ _Solidago petradoria_ _Koeleria cristata_ _Lupinus argenteus_ _Yucca baccata_ _Phlox hoodii_ _Eriogonum racemosum_ _Eriogonum umbellatum_ _Cordylanthus wrightii_ _Pedicularis centranthera_ _Penstemon linarioides_ _Penstemon strictus_

Two traplines were run from July 9 to 12, 1962, in the area south of the Bobcat Canyon drainage at an elevation of 7,100 feet. No mice were caught in three nights of trapping. Four additional lines were established on July 24, 1962, and were run for three nights, in the area north of the Bobcat Canyon drainage at elevations of 7,100 to 7,150 feet.

_P. maniculatus_ and _P. truei_ were caught here (Table 1). This vegetational a.s.sociation may have few rodents because there is a shortage of places where they can hide. Although _Poa fendleriana_ is abundant, the lack of shrubs leaves little protective cover for mammals.

_Mug House--Rock Springs_

A juniper-pinyon-mountain mahogany a.s.sociation extends from the area of Mug House to Rock Springs, on Wetherill Mesa. On that part of the ridge just above Mug House, the understory is predominantly _Cercocarpos monta.n.u.s_ (mountain mahogany), but northward toward Rock Springs the understory changes to _Fendlera rupicola_, _Amelanchier utahensis_, _Cercocarpos_, and _Purs.h.i.+a tridentata_. The ground cover is essentially the same as that in the pinyon-juniper-muttongra.s.s a.s.sociation described previously.

Four traplines were run from July 31 to August 2, 1962, and from August 13 to 15, 1963. These lines ran northwest-southeast, starting 1,000 feet southeast of, and ending 3,000 feet northwest of, Mug House. The lines traversed elevations of 7,225 to 7,325 feet. Individuals of _P.

maniculatus_ and _P. truei_ were caught here (Table 1).

Deer and rabbits inhabit the trapping area. Bobcats have been seen, by myself and by others, near Rock Springs. Lizards of the genera _Cnemidophorus_ and _Sceloporus_, as well as gopher snakes were seen in this area.

_Juniper--Pinyon--Bitterbrush_

Three pairs of traplines were run from August 7-9, 1962, in a juniper-pinyon-bitterbrush stand on the southern end of Wetherill Mesa, starting 200 yards southwest of Double House (Fig. 1).

The forest on the southern end of the mesas consists of widely-s.p.a.ced trees, which reflect the low amounts of precipitation at these lower elevations. Juniper trees are more numerous than pinyons, and both species are stunted in comparison to trees farther north on the mesa.

_Purs.h.i.+a tridentata_ (bitterbrush) is the understory codominant.

_Artemisia nova_ (black sagebrush) is present and gra.s.ses are the most abundant plants in the ground cover. Herbaceous species in the spa.r.s.e ground cover include the following:

_Opuntia polyacantha_ _Solidago petradoria_ _Lathyrus pauciflorus_ _Penstemon linarioides_ _Lupinus caudatus_ _Yucca baccata_ _Phlox hoodii_

Only _P. maniculatus_ was caught in this stand; all mice were caught in the first night of trapping.

Five areas were selected for trapping in the summers of 1963 or 1964, in order to test hypotheses concerning habitat preferences of each of the species of _Peromyscus_. Four of these areas appeared to be ideal habitat for one species, but not for the other. The fifth area was expected to produce both species of _Peromyscus_. Each of these areas is discussed below.

_One Mile Southeast of Park's Entrance_