Geology
The Sangre de Cristos are fault-block mountains with major fault lines running along both the east and west sides of the mountains and, in places, cutting through the range. The mountains were pushed up between 20 and 5 million years ago, basically as one large mass of rock. The Sangre de Cristo range is still being uplifted today as faults in the area remain active.
On the west side is the San Luis Valley a portion of the Rio Grande Rift. On the southeast side is the Raton Basin, a quiet but still active volcanic field. On the northeast side are the Wet Mountains and the Front Range, areas of Precambrian igneous and metamorphic rocks formed during the Colorado orogeny some 1.7 billion years ago and then uplifted more recently during the Laramide orogeny.
The Blanca Massif is also Precambrian rock, while most of the rest of the Sangres is composed of younger Permian-Pennsylvanian (about 250-million-year old) rock, a mix of sedimentary conglomerates, shales, and igneous intrusions. These sedimentary rocks originated as sediment eroded from the Ancestral Rocky Mountains.
Read more about this topic: Sangre De Cristo Range