The region’s geologic history, featuring confrontations between massive continental bodies over billions of years and yielding explosions many times larger than the hydrogen bomb, eclipses any human dramas by sheer scale.
The North American Craton is one of the oldest and largest continental formations on earth (600 million years old, spanning from the middle to the furthest north and east ends of the continent). This landmass gained its supremacy, it is hypothesized, by smothering a rival: the Farallon plate, which now lies subducted beneath the coast of present-day California. Yet, the energy expended to dominate the Farallon exacted a potentially-fatal price upon the Craton, causing it to deform, destabilize, and detach west of the present-day Rocky Mountains. (Mountains which resulted from this destabilization.)
Not only did the subduction of Farallon cost the Craton its integrity, it also gave birth to a new challenger: the Colorado Plateau. As Farallon sank into magma, it pushed this large slab of a Plateau—which encompasses most of the Four Corners region, beginning in Abiquiu—above the effects of destabilization.
The Colorado Plateau and the North American Craton have been facing each other down—circling slowly and at a distance—for 35 million years. The space between them has formed the Rio Grande Rift, which begins in Abiquiu and through which the namesake river flows. Every so often, the tension between the two contenders reaches a breaking point, and a volcano explodes—or a magma chamber, as in the case of the Valle Caldera.