This physiographic region is represented in Tamaulipas by a small part
of the long Sierra Madre Oriental that extends from the Big Bend area
in Texas southward to the Trans-volcanic Belt of central Mexico. The
Sierra Madre Oriental is in the southwestern part of Tamaulipas. The
Sierra was formed by folding of the Middle and Upper Cretaceous and
Cenozoic deposits that now are 400 to 2700 meters in elevation. In
general, the soils are Chernozems.
This physiographic region is situated between the other two
physiographic regions in Tamaulipas and represents a barrier to the
distribution of some tropical mammals on the one hand and to those from
the Mexican Plateau on the other.
[Illustration: FIG. 1. Three physiographic regions: 1 Coastal Plain; 2
Sierra Madre Oriental; 3 Central Plateau.]