This Province occupies all of the Sierra Madre Oriental and, therefore,
the southwestern part of the state.
The vegetation in general is Pine-oak Forest, in which the most common
trees are _Abies religiosa_, _Pinus flexilis_, _P. patula_, _P.
montezumae_, _P. teocote_, _Populus tremuloides_, _Juniperus
flaccida_, _Quercus arizonica_, _Q. clivicola_ and _Q. polymorpha_.
In his study of plants of the Gomez Farias area, Martin
(1958) recorded several different types of vegetation, which
in part can be placed in the Potosian Biotic Province,
especially those types that occur to the northwest of the
Cloud Forest. In addition to the Cloud Forest, Martin
recognized Humid Pine-oak Forest, Dry Oak-pine Forest,
Chaparral, Thorn Forest and Scrub, and Thorn Desert.
The only mammal endemic to the Potosian Province in
Tamaulipas is _Cryptotis pergracilis pueblensis_. Other
mammals that occur mainly in this Province are: _Sorex
saussurei_; _Notiosorex crawfordi_; _Glaucomys volans
herreranus_; _Cratogeomys castanops planifrons_;
_Perognathus nelsoni_; _Liomys irroratus alleni_;
_Reithrodontomys fulvescens griseoflavus_; _Microtus
mexicanus subsimus_; _Ursus americanus eremicus_; _Conepatus
leuconotus texensis_; and _Odocoileus hemionus_.
The fauna of this Province is a mixture of elements with
tropical affinities on the east side of the Sierra Madre and
with those of the Mexican Plateau on the west side.