This pocket mouse is restricted to the coastal sage scrub association,
and was recorded from Cajon Wash west to Live Oak Canyon. The mouse does
not inhabit even the lower edge of the chaparral belt, but in the
coastal sage flats is usually the most abundant rodent. In disturbed
parts of the coastal sage belt _fallax_ is less common, and was never
trapped in channels of rocky washes. Trap lines in the eroded adobe
banks of the foothills, where white sage and coastal sagebrush are the
dominant plants, took mostly these pocket mice. Although the soil of
such slopes is compact and seemingly is unsuitable for burrowing by
heteromyids, _fallax_ is the most common rodent. Because few burrows of
pocket mice were noted there, it is possible that the many old unused
burrows of _Spermophilus_ and _Dipodomys_ which honeycomb certain parts
of adobe banks are used also by _fallax_; some of these burrows
shelter _Peromyscus eremicus_ and _Peromyscus californicus_.
These mice are inactive above ground in cold weather. In the sage belt
near Thompson Canyon, where this subspecies had been found to be the
most common rodent, none was trapped on the sub-freezing night of
December 3, 1948, although other rodents were found in usual numbers.
Individuals have been taken on nights of intermittent rain, yet none has
been trapped on freezing nights.
This species is characteristically heavily infested by a large species
of mite. Usually these mites congregate around the base of the tail.
On October 11, 1949, one lactating female and two carrying embryos were
taken.
_Specimens examined._--Total, 11, distributed as follows: Los
Angeles County: 4 mi. N and 1 mi. E Claremont, 1900 ft., 5; 3
mi. N Claremont, 1600 ft., 6 (5 PC).
=Perognathus fallax pallidus= Mearns