mountains of southeastern
Coahuila, where desert shrubs are absent, roots and leaves of
low-growing forbs are eaten.

Three distinct habitats for _C. castanops_ occur in Coahuila. The
state is crossed by a series of mostly impassable, mountainous ridges
beginning at the northwestern boundary at the Canon de Boquillas on
the Rio Grande and extending southeastward to the east-central border.
This divides Coahuila into a more humid and less elevated northeastern
area which is an inland extension westward of the Coastal Plain and a
more arid and higher western and southern area which is a part of the
"Mesa del Norte" of the Mexican Plateau. In the extreme southeast the
still higher elevated plains and intermontane valleys within the
Sierra Madre Oriental afford a third habitat for populations of this
species. The subspecies of these pocket gophers found in any one of
these three habitats show greater affinity to each other than they do
to any subspecies found in the other habitats.

Generally speaking, populations of _C. castanops_ from northeastern
Coahuila are related, as a group, in color and cranial features.
Partial isolation of subspecies in this area results chiefly from
discontinuity of suitable soils rather than from topography. These
pocket gophers occur most commonly in the deep, sandy soils which are
found along streams, especially where farm lands are irrigated. In
western and southern Coahuila, mountains extending in both north-south
and east-west directions act as partial barriers to the passage of _C.
castanops_. Within this large area, pocket gophers occur in desert
basins many of which are enclosed on two or more sides by mountains.
Even so, with the exception of the smaller _C. c. consitus_ of
northwestern Coahuila, all known subspecies occurring at lower
elevations in the western and southern part of the state show close
relationships in color and cranial features. Those subspecies in the
higher parts of southeastern Coahuila by their small size and dark
color reflect to a high degree their isolation in an elevated habitat.

Males of _C. castanops_ differ greatly from females of equal age;
consequently animals of the same sex, as well as of the same age, are
used herein for taxonomic comparisons. Since, of any given age-group,
females show less individual variation than do males, we have relied
more on the characteristics of the females in this taxonomic study.
Only specimens taken at approximately th