The Amarillo Mountains are a buried granitic mountain range that is basically an extension of the Witchita Mountains in Oklahoma. You mentioned a book that claimed all mountains are the same age. We can look at several different mountain ranges within the United States to examine that premise. We have the Appalachians which are the remnants of at least three major mountain chains that have been eroded down to where the mountains are formational remants of the original range - the reistant formations form the mountain ridges. We have the Rockies, which, not even counting their previous incarnations, were uplifted during the Laramide Orogeny, eroded down to where they were buried up to their chins in debris, and then uplifed and exhumed - to where there is an old peneplain or erosional surface up about 8,000 feet in the Colorado and Wyoming Rockies. We have the Sierras, which are a young mountain range. We have a section of the Appalachians which are missing - from Alabama to SW Arkansas - which rifted off and have subsequently been found in South America due to plate techtonics. And then there are the Amarillo Mountains - which formed, eroded, and have been buried by younger sediments - all while other mountains still exist at the surface.
But somehow that assemblage of mountains is all of the same age? I don't think so.
I thought when driving through that the Ozarks looked just like the Appalachians except for the armadillos.
No names? No sneering? I might have to consider your thoughts.
The Sangre de Christo's seem to be rather young; the Jemez even more so. Paracutin is young too.