Only once was this mouse found outside the pinyon-juniper association of
the desert slope; in November, 1949, several were collected near Cajon
in mixed manzanita, scrub oak, and greasewood chaparral. This was the
only _Peromyscus_ of regular occurrence in the pinyon-juniper area, and
was recorded from the upper limit of this association, near Jackson
Lake, at 6000 feet, to the lower limit of the association at the mouth
of Graham Canyon at roughly 4000 feet elevation.
Although in the juniper belt _truei_ often occurs on common ground
with _Peromyscus maniculatus sonoriensis_, the habitat preferences of
these animals are generally complementary. Where the mice occur
together, traps set in a variety of locations caught _Peromyscus
maniculatus_, but typically traps set amid the brush or on the open
ground away from the junipers were productive. On the contrary _truei_
was invariably trapped quite near the junipers and often in association
with the large nests of _Neotoma fuscipes simplex_. In fact traps set
right on the beds of litter beneath the junipers were most likely to
catch _truei_. Records kept of trapping localities show that _truei_ was
without exception trapped within twenty feet of some treelike shelter
such as junipers, pinyons, Joshua tree or scrub oaks. Thus _Peromyscus
maniculatus_ occupies the open stretches between the trees, while
_truei_ inhabits the ground beneath and immediately adjacent to the
trees. In Nevada the pinon mouse prefers rocky areas (Hall, 1946:520).
In the San Gabriel Mountains this mouse does not seem to have this
predilection.
In the juniper belt _truei_ was second to _Dipodomys panamintinus_ in
point of numbers. In the course of 500 trap-nights in the juniper belt
twenty-two _truei_ were taken with thirty-six _Dipodomys_.
I consider my series of _Peromyscus truei_ from the desert slope of the
San Gabriels to represent the subspecies _montipinoris_. The series is
closely comparable to specimens of the subspecies _montipinoris_ in the
California Museum of Vertebrate Zoology from the Mount Pinos area, but
differs from specimens of the race _chlorus_ from the San Bernardino
Mountains in certain diagnostic characteristics. In his recent paper on
_Peromyscus truei_, Hoffmeister (1951) considered the populations of
this species in the San Gabriels to be of the race _chlorus_.
Hoffmeister had only one specimen available from the San Gabriel
Mountains (Lytle Creek, on the Pacific slope) which was intermediate
between _montipinoris_ and _chlorus_, but on the basis of cranial
measurements it was referred to the race _chlorus_. Specimens of
_Peromyscus truei_ from the eastern end of the desert slope of the San
Gabriel Mountains and the Cajon Pass area would probably demonstrate
that the race _montipinoris_, which occupies the desert slope of the San
Gabriels, intergrades with the race _chlorus_, which occurs in the San
Bernardino Range immediately to the east, in the Cajon Pass area.
Although _montipinoris_ occurs on the desert slope of the San Gabriels,
_chlorus_ may occur on the Pacific slope. I took no specimens of the
pinon mouse on the Pacific slope of the San Gabriel Mountains.
In December, 1948, many small juveniles were taken in the juniper
belt, and on October 15, 1951, two females trapped at the head of
Grandview Canyon had embryos: one three and the other four. On November
13, 1951, a partially gray-pelaged subadult female was trapped which had
recently suckled young.
_Specimens examined._--Total, 17, all in Illinois Museum of
Natural History, distributed as follows: Los Angeles County:
Mescal Canyon, 4500 ft., 8 mi. SE Llano, 11; Mescal Canyon, 4300
ft., 2; 6 mi. SE Valyermo, 5100 ft., 1; Grandview Canyon, 6 mi.
SE Valyermo, 5100 ft., 1. San Bernardino County: 1 mi. W Cajon,
3200 ft., 2.
=Onychomys torridus pulcher= Elliot