western Texas it is common at the upper edge of the arid Lower Sonoran
Zone, and in this region does not enter the Upper Sonoran to any extent.

In July, 1914, Goldman found this kangaroo rat common on the plain at
4,600 feet altitude, near Bonita, Graham County, Ariz., and noted a few
as high as 5,000 feet altitude on the warm southwestern slopes of the
Graham Mountains, near Fort Grant. Apparently _spectabilis_ reaches its
upper altitude limit in the Burro Mountains, N. Mex., where Bailey has
found it sparingly on warm slopes up to 5,700 feet, and at the western
base of the Sandia Mountains, east of Albuquerque, N. Mex., where dens
occur at approximately 6,000 feet.

About Tucson it is undoubtedly more common in the somewhat higher
portions of the Lower Sonoran Zone, above the _Covillea_ association,
than elsewhere (Pl. IV, Figs. 1 and 2). A few scattered dens are to be
seen in the _Covillea_ belt, but as one rises to altitudes of 3,500 to
4,000 feet, and the _Covillea_ is replaced by the cat's-claws (_Acacia_
sp. and _Mimosa_ sp.) and scattered mesquite (_Prosopis_), with the
_Opuntia_ becoming less abundant, kangaroo rat mounds come more and more
in evidence. Here is to be found the principal grass growth supporting
the grazing industry, and the presence of a more luxuriant grass flora
is probably an important factor in the greater abundance of kangaroo
rats, both _spectabilis_ and _merriami_. In this generally preferred
environment the desert hackberry (_Celtis pallida_) is one of the most
conspicuous shrubs; clumps of this species are commonly accompanied by
kangaroo rat mounds.

In order to ascertain whether the banner-tailed kangaroo rat has any
marked preference for building its mounds under _Celtis_ or some other
particular plant, all the observable mounds were counted in a strip