Underlying the Permian rocks of the West Texas basin are the roots of a Paleozoic mountain range. In direction of strike and structure the folds of the mountains bear a general resemblance to the mountains of central Colorado. However, the Permian and younger rocks of the West Texas basin were not refolded during the early Tertiary as were the ranges of central Colorado. In this paper, the writer attempts to show the reason for this difference in tectonic history which has resulted in the absence of a folded front range province from northern New Mexico as far S. as the Sierra Madre Oriental in the Republic of Mexico. In the course of the investigation paleogeologic maps were constructed of the area from Big Bend of Texas to central Colorado for the beginning of Pennsylvanian and the beginning of Permian time. From these a tectonic map showing elements existing at the beginning of Permian time was built and compared with a similar map showing present elements. Cross sections were made comparing homologous tectonic units of the West Texas basin with the Cordillera of central Colorado. In this manner the writer has come to the conclusion that the pre-Permian folds of the West Texas basin are not tectonically related to the younger folds of central Colorado although they do have certain characters in common. The Paleozoic rocks of the 2 areas were laid down in different basins separated by the Precambrian massifs of the continental backbone throughout most of Paleozoic time. These massifs, together with the tightly folded Paleozoic rocks of the Marathon-Ouachita belt, absorbed and distributed Laramide stresses and preserved the West Texas Permian basin from early Tertiary mountain building in spite of the presence of structural and sedimentational features favorable to mountain building.

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