The Scenery North of Santa Fe Hides a Fascinating Story
Northern New Mexico offers some of the most stunning scenery in the Western US. There are higher mountains elsewhere, and deserts with more unusual cacti, but the blending of landscapes, the expanses of basins and mountains and rivers patiently sneaking past the dry expanses offer anyone who looks around a wonderful array of color and light and mystery.
In our short lives, it is easy to see the land as it is and assume it has always been that way and may stay the way it is for a long time. But, land is not static, it is not a painting, it is masses of change happening over vast, inconceivable stretches of time. Having worked in environmental education for decades, I know that most people recoil from the abstraction of millions of years, and most people don’t think about or understand the geologic past. I don’t fault anyone for this as people from much of the world confront a mass of vegetation in their regions, the geology safely hidden under trees, moss and brush. And most people are busy with ideas more immediate than questions.
Here in New Mexico our arid climate leaves the features of the land exposed and open to scrutiny. The rains erode the land rapidly and move its dirt, sand and gravel around, ultimately sending vast amounts of it down the Rio Grande toward the Gulf of Mexico where it has been dumped on the ocean floor for millions of years. Humans have hastened this erosion by unleashing livestock across the landscape. What little grass was in the valleys was consumed by cattle and sheep and the open soils washed away, leaving the subsoil exposed.
Look at the big mountains above Santa Fe and Taos. These are made of rocks more than a billion years old, thrust from deep in the earth upward over the last billion years by the forces of continental movements. They are capped with younger rocks, only 300 million years old that have the impressions of marine shellfish embedded in their broken surfaces. Billion-year-old rocks covered with limestones and shales from ancient oceans, thrust up to 10,000 feet above sea level today, well away from any contemporary ocean.
Look at the mountains above Los Alamos and Bandelier National Monument. This gentle range is a volcano that last erupted violently just over a million years ago, blasting ash and rock into the atmosphere in a huge eruption that laid down beds of ash that form the sculpted mesas in and around Los Alamos and Bandelier National Monument. The Jemez Volcano bulged up from the landscape around 12 million years ago and had hundreds of moderate eruptions over time, and it likely will erupt again, probably after humanity is gone.
Between these two mountain ranges, big beds of soft brown rocks form most of the near scenery from just north of Santa Fe almost to Taos and Abiquiu. These brown sands and rocks form Camel Rock and the buttes and hoodoos that gather against the base of the Sangre de Cristo Mountains through Nambe and Chimayo and north to Embudo where younger lava flows cover them up. It is safe to say that these brown rocks and sand, called the Santa Fe Group by geologists, extend under the Pajarito Plateau on the flanks of the Jemez Mountains and they extend under the young volcanos west of Santa Fe, the Caja del Rio Volcanic Field.
Where did all these brown landscapes come from? It turns out that long before the Rio Grande and the Rio Chama flowed through New Mexico, flat basins existed from southern Colorado to well south of Albuquerque. These flat basins collected the sands and gravels that flowed off the Sangre de Cristo mountains for the last 17 million years. The Sangre de Cristos Mountains have large amounts of brown granite that forms the lower flanks of the mountains above Santa Fe, and Chimayo. These granites and other rocks have eroded with streams down into the valley to form the brown Santa Fe Group rocks that dominate the landscape from Santa Fe north.
Those closed basins with flat bottoms had lakes that came and went and they were covered with a five-foot-thick layer of fine volcanic ash from a super volcano eruption far north of here 17 million years ago when the Yellowstone area was being rocked by massive volcanic eruptions. So much ash came from these distant eruptions that it blanketed the landscape over large areas. While most of it eroded away, here in the Santa Fe Group the white band of this ash is clearly visible in many places, down among younger layers of mountain sediments. The ash was covered with more local brown sediments after the end of those distant eruptions. The bed of ash gives us a good reference line as we look at how the sediments have tilted and eroded over the millions of years.
Today the Santa Fe Group, also called the Tesuque Formation, are no longer flat like they were when the ancient basin filled with stream debris from the mountains. As the land has gradually expanded to the east and west, the whole basin of sediments has tilted to the West. When you are driving from Nambe to Chimayo you can see the straight lines in the cliffs that now tilt downward. Millions of years of rain have sculpted the landscape into the spectacular “desert” we see today.
Stop, if you can, and take a walk into the wilderness of bluff, arroyos, cliffs, faults, and hoodoos. Even if you are baffled by the geologic history, enjoy the basic reality that we are living in a constantly changing landscape that will look vastly different than it does now thousands of years in the future when humans are gone and the natural world has slowly rebuilt itself from the massive environmental destruction that people are causing today including mass extinctions of wildlife, tremendous amounts of plastic waste, and air pollution that is changing the climate with extreme effects on the land and oceans.
This is a beautiful region and knowing the basic geologic story can make the scenery come alive in your imagination. The wonder of it all is dazzling.
