The main range of this mouse in the San Gabriel Mountains lies between
1600 and 6000 feet elevation on the Pacific slope of the Mountains, thus
encompassing much of the chaparral and oak woodland associations. It
was the most common mammal in the oak woodland association in the lower
foothills and often was trapped there on leaf mold beneath the oaks.
While trapping for shrews I regularly took this species in riparian
growth right down to the edge of the water. In San Antonio Canyon many
_boylii_ were trapped beneath logs and dense vegetation, and on wet
seepage slopes adjacent to the creek.
This species shows a definite predilection for rocky habitats where
these occur in the chaparral. In heavy lilac brush near Camp Baldy
_Peromyscus boylii_ was outnumbered by _P. californicus_, yet where
talus slopes or boulder piles occurred _boylii_ was more numerous. At
the head of Cow Canyon amid boulders beneath scrub oak, bay, and big
cone-spruce, this species was especially abundant and no other
_Peromyscus_ was taken.
Of special interest is the occurrence of this mouse on the desert slope
of the mountains; there it was taken beneath scrub oaks in the
pinyon-juniper association at the mouth of Mescal Canyon, and amid
boulder and debris piles in Mescal Wash at 4000 feet elevation. While
manzanita and scrub oak grew in the wash at the points of capture, the
animals were actually surrounded by the desert conditions of the Joshua
woodland, and associated with such desert forms as _Onychomys torridus
pulcher_ and _Peromyscus eremicus eremicus_.
Immature individuals were taken in October, November, February, and
March, and a female with two large embryos was taken near Icehouse
Canyon on November 8, 1951.
_Specimens examined._--Total, 8, distributed as follows: Los
Angeles County: Mescal Wash, 4000 ft., 1; Mescal Canyon, 4800
ft., 2; San Antonio Canyon, 5200 ft., 2; San Antonio Canyon,
4500 ft., 1; San Antonio Canyon, 2800 ft., 1; Thompson Canyon,
1800 ft., 1 (PC).
=Peromyscus truei montipinoris= Elliot