Fifty million years ago titanic forces below the surface pushed a 30 by 60 mile ridge upward, and affected the surrounding rock and soil layers from Chaco Canyon to Quemado in a north south area. The Zuni Mountains were then born. The tremendous forces needed to move such an area of the Earth’s surface originated with the movement of the North American continental plate. The plate in those times was moving generally westward at a rate similar to the speed of your growing fingernails. Many miles under the surface, where the crust and mantle meet, the junction is not smooth and flat. There are many irregularities that can slow or redirect the motion of the massive crustal plate. But the plate is huge and if its motion is altered, the result can be bending, also known as folding; up, down, or sideways, or breaking; also known as faulting. Again, up, down or sideways. There did happen to be some blockages to the plate’s motion back in the late Jurassic to Cretaceous time, 70-50 million years ago. There was a remnant slab of hardened basalt, a kind of solidified lava in the crust left from the upwelling of mantle material during the formation of the lava fields that make up the Mogollon Rim in Arizona and New Mexico. A long rod shaped piece of this basalt (called the indenter - Chamberlin and Anderson, 1989) that reached from near Morenci, Arizona to just about the Quemado, New Mexico area lay waiting a few thousand feet below the surface. There was another curious impediment to the moving crustal plate. The hot mantle below the crust is in a molten plastic state partly because of the pressure placed upon it by the force of gravity pulling down the overlying crust. The heat in the mantle also comes from the decay of radioactive materials in the interior of the planet. This heat causes the hot mantle material to circulate; slowly, but there is movement. In certain areas of the Earth’s underlying mantle, there is upwelling motion, and in other areas, downward motion. Upwelling occurs in hotter than average mantle, and downward motion occurs in cooler than average mantle. Just like hot air or hot water moving in relation to the surrounding air or water because of its density. Anyway, there was this upwelling of hot mantle just as the crust which carried the southwestern U.S. passed over. The upwelling forced the moving crust to slow its motion, as it had to ride up and over the slight bulge on the hot rising mantle below. This caused the crust to thicken, bend, and crack as the change in motion was transferred back to the crust still pushing from behind. Finally, there was another significant force interfering with the crust in this area. The Pacific plate, another large crustal mass moving as a unit, was moving east to northeast directly toward the North American plate. In fact they were already in contact, and pushing against each other. This plate boundary today is seen in the San Andreas fault, and the so called “ring of fire” that runs from the southern tip of South America to the Aleutian islands of Alaska. We see intense crustal violence from earthquakes to volcanoes occur all along this boundary today as well as it must have occurred in the past. So, these three forces worked together to crumple the crustal plate in the region where the Zuni mts. would form and weaken the crust with folds and faults. It must be stated that the area where the mts. would form was covered with 10 to 15 thousand feet of sediments that had been laid down by wind, water, and other forms of erosion over the previous 300 million years. The overlying sediment was roughly similar in strength, but the underlying basalt indenter rod was much harder and resistant to force. The underlying pressures compressed the local area from SW to NE, which served to compress or shorten the crustal sediments, but did not compress the basalt indenter rod. The basalt in effect pushed from the SW and compressed the sediments in the vicinity of the Zuni mts. The sediments buckled, and bent, then broke or faulted and giant slabs of crust were pushed upward and to the NE, and stacked up against each other This compression uplifted the Zuni mts. into a giant upfold or anticline. The indenter was twisted from a horizontal motion to a more vertical motion as it compressed the sediments. The basalt indenter rod’s leading edge is exposed today as a dark meta-gabbro rock mass in the central part of the uplift. Then at least 15000-20000 feet tall, and today eroded to 9000 feet, the erosion has worn down, and exposed, all the rock layers that used to cover the area. The deformations caused 15-mile long rock slabs to overlap, slide, tilt, and push the adjacent rock masses in all directions resulting in an uplifted, elliptically shaped region of deformation 60 miles by 30 miles in size. Many neighboring areas of rock, while not faulted and folded, were tilted up from the horizontal giving us the cuestas and mesas of today. Harder more resistant rock layers formed ridges and mesas, while the softer more easily eroded rock layers are where the lowlands and valleys are today. Both ridges and valleys ring the Zuni Mountains. Today, the regionally arching rock layers have been dissected by erosion and show us all, the sequence of rocks that built the area, from the arch building indenter, to the surrounding metamorphosed granite basement layers, to the sediments that were exposed by subsequent erosion, and finally the lavas that flooded the low areas as the cracked, faulted rocks leaked material from below.