What section of Texas is mostly mountainous?

The section of Texas that is mostly mountainous is the Trans-Pecos region, located in the far west of the state. This area includes the Davis Mountains and the Guadalupe Mountains, which are home to the highest peaks in Texas, such as Guadalupe Peak. The region features a diverse landscape with rugged terrain, canyons, and desert scenery. It is also part of the larger Chihuahuan Desert ecosystem.