Final answer:
El Paso is the major Texas city nearest to the oldest rocks in Texas, which are part of the Precambrian formations in the Franklin Mountains.
Step-by-step explanation:
The major Texas city that is nearest to the oldest rocks in Texas is El Paso. These ancient rocks, which are part of the Precambrian rock formations, can be found in the Franklin Mountains to the northwest of the city. The Franklin Mountains are considered to be part of the larger chain known as the Rocky Mountains and are estimated to be about a billion years old. Therefore, when looking for the oldest geological formations within the state of Texas, we point towards El Paso as the nearest major city to this ancient and fascinating history encoded in stone.