Sierra Nacimiento

This article will consider them as a unit together with the San Pedro Mountains, which are a smaller range contiguous with the Sierra Nacimiento on the north, and which are also part of the Nacimiento Uplift[2] and lie at the edge of the greater San Juan Basin, which sits atop the Colorado Plateau.

The corresponding range on the east side of the rift, the Sangre de Cristo Mountains, is significantly higher and more rugged than the Nacimientos, which consist of long, gentle ridges never reaching above tree line.

The Jemez Mountains lie between the Nacimientos and the Sangre de Cristos and are sometimes mistakenly thought to be part of the structure of the rift, but in fact are of volcanic origin rather than part of the graben of which the Nacimientos and Sangre de Cristos are the obvious manifestations.

The San Pedro Mountains are a high plateau that geologists interpret as an old erosional surface.

This is overlain by remnants of the Pedernal Chert and Ritito Conglomerate, which are relatively young geological formations.