Final answer:
North Texas, including the Dallas-Fort Worth area, is part of the Great Plains, which is a flat and agriculturally important region. It is not in the reaches of the Rocky or Appalachian Mountains.
Step-by-step explanation:
The formation found in the north Texas (Dallas-Fort Worth area) is the Great Plains. This area of Texas is part of the vast Interior Lowlands and the Great Plains, characterized by its relatively flat landscape and staple in American agriculture. Neither the Rocky Mountains nor the Appalachian Mountains are located in this region. Instead, the Dallas-Fort Worth area is situated in the southern part of the Great Plains, which extends into Texas from the north.