What is so special about the Cascade-Siskiyou National Monument?

This national monument spans the border between Oregon (Jackson County) and California (Siskiyou County) immediately east of the I-5 freeway. It was first established in 2000 by President Bill Clinton and expanded in January 2017 by President Obama as one of his last actions before leaving office. The monument is managed by the Bureau of Land Management (BLM) from the local Medford Oregon office. It is an important time to learn more about the monument because it is one of the four that Interior Secretary Zinke (Trump administration) has proposed to shrink. 

Several weekends ago, we hiked to Hobart Bluff in the monument with Mike and Chris from the San Francisco Bay Area. This view (with Jay and Mike) is to the northwest, parallel to the Bear Creek arm of the Rogue Valley, with Emigrant Lake in the near part of the valley and the buildings of Ashland just beyond the lakes. To the west of the valley (left side of photo) are the Klamath Mountains that consist of old Paleozoic and Mesozoic, mostly oceanic, rocks that were added to the continent many tens of millions of years ago. To the east of the valley (right side of photo) are the mountains that make up the Western Cascades—the now-eroded volcanoes that were active from about 40–15 million years ago. The currently active volcanoes are located just east of the Western Cascades; although they didn’t show up well in photographs, Mt. McLoughlin volcano was visible to the east and Mt. Shasta volcano was visible to the south.

So why was this area declared a national monument by President Clinton in the first place? Turns out this monument was the first to be recognized solely because of a desire to preserve its incredible biodiversity. In recognition of this biodiversity, the region has also been designated as an Area of Global Botanical Significance and proposed as a World Heritage Site and UNESCO Biosphere Reserve. 

And what is the cause of all this biodiversity, you may ask? Well, it’s all about the geology, of course! This location is at the intersection of the Cascade, Klamath and Siskiyou mountain ranges, with additional climatic influences from the Basin and Range province to the east (starting at Klamath Lake) and the Pacific coast to the west. These rugged mountain ranges are characterized by a complex suite of rock types that creates the various soil types, topographic changes, and micro-climates that produce so many diverse ecological niches. David Rains Wallace’s 1983 book about the natural history of the region (biological and geological), entitled “The Klamath Knot”, produced a visual way (a knot) to think about this complexity.

Clearly, there are many good reasons for preserving the natural environment of this region. As it is, there remain many private holdings within the monument, and the law allows for recreational activities such as hunting and fishing. In fact, our hike was curtailed by gun shots as we attempted to continue south to Soda Mountain. Only very limited commercial interests are likely to benefit from the monument’s shrinkage and it is my hope that the monument will remain at its current size so that more of the public can enjoy its bounty and beauty.

For more information :

—BLM site with photos and useful information: https://www.blm.gov/programs/national-conservation-lands/national-monuments/oregon-washington/cascade-siskiyou

—Site of Friends of the Cascade-Siskiyou National Monument, a group that organizes hikes and other activities in the monument and strives to protect it: http://www.cascadesiskiyou.org/

—World Wildlife Fund’s site about the area’s global significance: https://www.worldwildlife.org/ecoregions/na0516

—Wikipedia site about “The Klamath Knot”: https://en.m.wikipedia.org/wiki/The_Klamath_Knot


The Great American Biotic Interchange

With its many excellent fossil sites, Argentina has lots of evidence for how life evolved through time. One of the largest effects on how organisms evolved was the position of the continents. For example, when the continents were united into the “super continent” called Pangea at the end of the Paleozoic, land animals could migrate for huge distances. In contrast, once the continents began to separate in the Mesozoic, animals could not move so far and so they evolved independently on the separated continents. 

One relatively recent change was between the continents of North and South America, which were separated by ocean until about 3 million years ago, when the Isthmus of Panama closed, and animals could start migrating between the continents. This resulted in what has been called “The Great American Interchange”. 

Many groups moved from North America to South America; for example, the great cats, including the Saber-toothed tiger (Smilodon genus—shown above). If you’ve been to the La Brea Tar Pits museum, you know that these tigers roamed the area that is now Los Angeles until about 10,000 years ago (they also went extinct in South America).  Other groups that moved south were elephants, bears, horses, deer, and camels. It’s interesting that camels subsequently went extinct in North America, but persist in South America as the camellid groups of llamas, vicuñas, guanacos, and alpacas.

Many groups also moved from South America to North America. One of the most interesting was the glyptondon genus (shown above) whose members were strange-looking herbivores that got as large as cars and that are now recognized as members of the armadillo family. Other groups that moved north included sloths, bats, porcupines, and various types of birds (including the “terror birds”).

Another interesting example is the giant ground sloth (megatherium genus—shown above) that was endemic to South America. When you go to Costa Rica to search for the shy little sloths that hang out in trees, it’s hard to imagine the elephant-sized animal that was the megatherium. You can see fossil remains of large sloths in North America (but not as large as megatherium) in the La Brea museum in Los Angeles. 

This biotic interchange caused extinctions in both North and South America, as new predators arrived in each continent to compete with the endemic fauna. But most of these so-called “megafauna” went extinct a mere 10,000 years ago, perhaps because humans had arrived and developed sophisticated enough weaponry to kill off the animals for food, sport, and/or safety. Paleontologists continue to debate the reasons.

All of the photos in this post were taken in the Museum of Natural Science in Córdoba. 

Earthquakes tell the story of changing tectonic plates along the Andes

We are now in Córdoba city (capital of the province of Córdoba), which is nearly 600 km (360 miles) east of the Cordillera Principal (high Andes). To the east of Córdoba are the flat plains of the pampa; to the west are the Sierras de Córdoba that, together with the other ranges lying eastward of the Cordillera Principal, are referred to as the Sierras Pampeanas, because they rise abruptly up from the flat pampa. Although reaching an elevation of almost 2900 meters (9500 feet), these sierras seem mere hills compared to the high Andean mountains to the west.

We have traveled through about 10 degrees of latitude, from north of Jujuy (23 degrees south) to Mendoza (33 degrees south). The Sierras Pampeanas are the mountains that extend east from the Andes from Tucuman to Córdoba. The Sierras de Córdoba are the mountains west of Córdoba city; they are very young, geologically speaking (less than 2 million years).

Why do these mountains extend so far east of the Andes? The Andes are produced by the convergence between the continental plate (South America) and the oceanic plate (Nazca), which is subducting beneath South America. In the Pacific Northwest of the U.S., an oceanic plate is subducting beneath North America, and we have the usual line of volcanoes (Cascade Range), but there are not additional mountain ranges located farther east. In Argentina, there are active volcanoes north and south of the Sierras Pampeanas, but not where these ranges extend so far east. We can look at the distribution of earthquakes to understand both the lack of volcanoes and the presence of subduction-related mountains so far to the east.

Notice that in the far north of Argentina, the earthquakes occur at shallow depths (red color) near the coast and are progressively deeper farther east (blue, then green for the deepest earthquakes). This is the expected distribution because the subducting ocean plate, which remains brittle and can store stress to create earthquakes, gets deeper and deeper as it is subducted farther beneath the continent. West of Córdoba, there are shallow (red color) earthquakes extending much farther east and there are no really deep (green color) earthquakes. This is because the oceanic plate is staying flat (so-called “flat slab”) and is not descending deep within the earth as it usually does.

These images are cross sections or profiles (perfiles) that show the two types of subduction. On the top is the normal distribution, with earthquakes getting deeper to the east, reflecting the steep inclination of the subducting oceanic plate. On the bottom is the “flat slab” distribution, with earthquakes at shallow depths, even at great distances from the subduction zone. Because the “flat slab” of the oceanic plate is not sinking much into the hot aesthenosphere, it does not cause melting and volcanoes. Because it is moving right beneath the continental plate, it affects this overlying continental plate and causes uplift within the plate, far from the subduction zone, along thrust faults. 

Why does this happen, you may ask? There are a variety of reasons, including age of the downgoing oceanic plate and whether or not the downgoing plate has ridges or seamounts that interfere with the sinking process. One reason the Andes have been studied so much is because we had a “flat slab” situation in the western U.S. about 65 million years ago, when mountain ranges formed farther east, but as a result of subduction along the coast, in the region that is now the Rocky Mountains. Studying mountains where “flat slabs” are happening today helps us to understand how they happened in the past.

In San Juan, we visited INPRES, El Instituto Nacional de Prevención Sísmica (http://www.inpres.gov.ar), which aims to keep people safe in a seismically active region. They focus on two goals: monitor the earthquakes that occur, and develop standards for building that will keep them from falling during earthquakes. The center is located in San Juan because they had a strong earthquake in 1944 that destroyed the whole town, where most buildings were constructed of adobe. The number of fatalities was huge and this city has focused much attention on making sure that buildings are reinforced and able to withstand shaking.

We met with a civil engineer who was passionate about the need for better building standards. The seismographs are historical relicts; today they have modern equipment and computers for earthquake monitoring. 

Argentina—a paradise for fossils of dinosaurs and proto-mammals

We visited Parque (park) Ischigualasto, which means “the place animals go to die” in the local indigenous language. The native people saw many bones in the region, which was the reason for this name. Later, of course, these bones were recognized as animals that have long been extinct. We also visited the Museo de Ciencias Naturales (museum of natural sciences) in San Juan, the capital of the province of San Juan where a variety of sites with dinosaur and other Mesozoic fossils have been found.

Here are the bones (some parts are reconstructions) of two giants found in the area around Ischigualasto that are now on display in the museum of natural sciences.

This area is called the “world-wide cradle of dinosaurs” because the earliest examples of dinosaurs have been found here. The incredible preservation and variety of animal bones have changed ideas about dinosaur evolution. For example, it was discovered that dinosaurs evolved more rapidly, and with a larger variety of species, than had been previously thought. 

Here is an example of one of the earlier animals, which are ancestors of the modern crocodile. But the early animals were much larger and lived on land rather than in water.

One of the surprising findings was a variety of so-called proto-mammals that had characteristics of both reptiles and mammals.  It was astonishing to learn that some these proto-mammals were quite large. They thrived toward the end of the Triassic, but most perished during the end-of-Triassic extinction. After the extinction, the dinosaur group expanded greatly throughout the Jurassic and Cretaceous Periods, whereas the mammal group was reduced to small numbers and sizes. The mammals got their revenge, though, when the end-of-Cretaceous extinction (the famous one that resulted from a meteorite impact in the Yucatán), destroyed all of the dinosaurs and the mammals found vacant niches to occupy, resulting in a huge expansion in their sizes and numbers throughout the Cenozoic Era.

This cute girl (ha!) had characteristics of both reptile and mammal. She fed her young just like mammals do today. Although we might not like the idea, she had many characteristics that we do and is on a direct line that eventually led to the human species!

In San Juan Province paleontologists also found dinosaur footprints, which are very rare. One type was of herbivore sauropods that are the largest dinosaurs ever found. The largest specimen ever found was in Argentina, but at a site farther south in Neuquén Province. It was named Argentinosaurus and was nearly 40 meters (~130 feet) long and weighed nearly 100 metric tons. 

In the natural science museum there is a replica of the sauropod’s belly and legs. It’s hard to imagine how much plant material this animal had to eat each day to sustain its huge bulk.

Although we couldn’t see any active excavation sites in Parque Ischagualasto, we did get to see the Triassic sedimentary formation within which these dinosaur fossils have been found. This photo shows the river deposits, which look much like the Morrison Formation in Colorado, where dinosaur fossils have also been found. The area is called “Valle Pintado” (painted valley).

The park has other interesting geologic feature (geoforms), such as round concretions that are formed by crystals of quartz or calcite that cement sand grains together to make a hard resistant rock. This area of concretions is called the “Cancha de Bochas” (bocce ball court).

We also visited the nearby Parque Nacional Talampaya, where Triassic-aged sediments have been eroded by water and wind into fantastic shapes. Note the white pickup truck for scale, in front of the sheer sandstone cliff.

Speaking of wind, we also visited Parque Nacional Leoncita, which is famous around the world for its pampa, which is a dried  lake bed that is a perfect place for the practice of carrovelismo (land sailing). Although the wind was not too strong on the day we visited, we still had a thrilling time operating the land-sailing vehicles. Here is our guide’s daughter Victoria, having fun.

And of course there are always the gorgeous colored rocks with Andes mountain backdrop.

The second highest mountain range in the world—and still rising

After the Himalayas, the Andes Mountains are the second highest range in the world—but you have to go to the right place. Many parts of the Andes are beautiful but have elevations more similar to other, relatively low-elevation subduction-zone ranges like the Cascades in the Pacific NW (USA). But at 6964 meters (22,841 feet), Alconcagua is the highest peak in the Western Hemisphere and part of an impressively vast range that continues north to the high plateaus of the Puna (Argentina) and the Altiplano (Bolivia) where many peaks reach heights of at least 6,000 meters. Along this distance of more than 20 degrees latitude (~13–33 degrees south) deformation associated with the Andes extends east for a considerable distance. We are traveling along about 10 degrees of this distance (~23–33 degrees south) in the Cordillera Oriental (eastern Andes) which is the part that is being thrust eastward into the non-mountainous part of the country. A future post will explain why this is happening but this post will show evidence for continuing rapid activity—not easy to show, but I’ll try!

Folds, folds everywhere, as shown on this Google Earth image in the Quebrada de Humahuaca. Because of the compression within this part of the Andes, thrust faults are pushing thick sequences of sedimentary layers eastward and causing them to buckle and fold and form spectacular exposures when eroded by the elemental forces of wind and water. But what is the evidence of a young age?

This photo shows sedimentary rocks (pinkish color) that are fairly well lithified (i.e., turned into rock) being thrust over younger alluvial fan deposits (grey color) that are not lithified. [The upper contact is the depositional contact of the fan gravels on top of the older pink sediments; the lower contact is the fault, where the older pink sediments have been thrust over the younger fan deposits.]  The fault must be younger than the fan deposits, which are certainly only some thousands of years old—super young in geologic time. My llama helped the photo by pointing his ears in the direction that the fault moved forward.

Another line of evidence is terraces that are former levels of a river that were uplifted by the actions of faults and folds; once the older river surface is at a higher elevation, the river has to carve a new flat surface. In the photo above, there are three obvious terrace levels at the lowest elevations, and there are at least three more at higher elevations that are less obvious because they are older and more eroded.

Alluvial fans are also common in areas of active land uplift—they act to carry sediment from the high mountain ranges to the river in the main valley. With high uplift comes steep slopes and severe amounts of erosion that produces copious amounts of sediments that can have very large sizes. We saw rock pieces in alluvial fan deposits that were as large as cars. Many of these alluvial fans have, in turn, been uplifted and eroded. This photo is looking down on the Quebrada de Humahuaca (view from east to west). The large fan on the left is currently being eroded by the Rio Grande (big river). 

Here is a view of what these alluvial fan deposits look like.

The overall feeling in this region is one of raw geology—the steep slopes, large-sized sediments, and deep erosion all leave the viewer with the feeling of a landscape in rapid change. 

If has been amazing to see many condors, who take advantage of the high elevations to soar on the thermals. Here is a photo taken by our guide Fede Norte (nortetrekking.com). 

And here is the exhilarating place we (photo of Fede, his daughter, and Jay) hiked up to and from which we could see the condors close up. Incredible!


Climate, culture and history of the Quebrada de Humahuaca

Because the Quebrada de Humahuaca is such a long north-south valley with readily available water from the river (Rio Grande) that cut it, it has been a well-used route connecting Peru, Bolivia and Argentina for thousands of years. The region was also important in the revolution for independence from Spain (1810).

To the west, the highest part of the Andes, called the Puna in Argentina and the Altiplano in Bolivia, is a moonscape where few people live. To the east, there are more mountains and the forests of Brazil and northeastern Argentina that capture most of the water being delivered by the westward-flowing trade winds. The Quebrada and Puna are quite dry, but still not as dry as the Atacama Desert on the western side of the Andes (in Chile) that gets almost no precipitation because of the strong rain shadow effect.

Cerro Miniques (above) is a volcano in Chile that is very close to the Argentina border. [This photo was taken in 2006 when we visited San Pedro de Atacama and the Atacama Desert while I was a Fulbright Scholar in Chile.] This volcano has an elevation of 5900 meters (19,300 feet); there are many equally-high, active volcanoes that extend north–south along the Chile/Argentian border. A little moisture gets to these highest elevations but almost none reaches the lower elevations of the Atacama Desert to the west.

The Quebrada of Humahuaca is located in the sub-tropics. It is easy to remember the latitude because the Tropic of Capricorn (23 degrees south) passes through the Quebrada.

Here we are (view to the west) at the marker between the towns of Tilcara (to the south) and Uquía (to the north).

Although this trip is mostly in the part of the Andes that is east of the Puna (Cordillera Oriental), we were fortunate to find an excellent guide—Victor Cuezzo (www.equipatuaventura.com.ar)—who drove us over a mind-bending pass to the Salina Grande in the Puna. The Puna has many salinas because of the closed, internally-drained valleys located between the mountains to the east and the volcanoes along the crest of the Andes to the west.

People have been using the salt in the salinas and trading it for other goods for thousands of years. At this location on the salina’s edge, we could see how the local community benefited by cutting the salt into blocks, putting the blocks into large bags, and selling it to others. The people were using the salt creatively, to make statues, and practically, to make buildings and souvenirs for tourists. Lithium is also found in some of the salinas but the local people are not in favor of this because the benefits go mainly to large international companies.

When we went trekking with the llamas, we had the good fortune of visiting Adela’s mother who lives even higher in the valley than her father. They get together sometimes, but Adela’s mother (at age 70) is fully occupied caring for a herd of about 150 goats and making artisanal cheese from their milk. The methods she is using go back many generations.

Adela’s mother with a large pail of goat milk and the starter she uses to make delicious, completely hand-made cheese. Although this method would never pass health codes in the United States, she takes great care to keep the cheese sanitary and sells the cheese in town (Tilcara).

To get salt for the cheese, she grinds salt from a block, probably derived from Salina Grande, using a flat rock for the mortar and a round rock for the pestal.

Although Adela now lives in Tilcara, and lived most of her adult life in Buenos Aires, she grew up in these mountains until the age of 16. From her grandmother she learned uses for many of the local plants, and even learned which rocks are best used for tasks such as cooking or making ceramics.

Here is Adela with the youngest member of the goat herd, who had to stay back while the adults went out to graze on pasture and the juveniles got fed alfalfa. We marveled at the fortitude of Adela’s mother, who works so hard every day to care for her goat herd, about 6 dogs, and some cats and chickens. Yet she seemed very happy with her life.

Victor also drove us to the remote town of Iruya, located east of the Quebrada and only accessed by a harrowingly narrow, winding road. The youthfulness of the landscape is in full view here—nearly vertical slopes and an extremely narrow valley formed by deep incision of the river—a clear indication that the land is rising now at a rapid rate. The eroded cliff on the left side of the photo consists of young alluvial fan deposits (some thousands of years old) with huge boulders that hover over the road. I would not want to be there in the rainy months when large boulders certainly fall onto the road and the sediments, mostly debris-flow deposits, get recycled again into debris flows that are potentially very dangerous.

People in Iruya still retain many of their ancient traditions, which they have melded with the cultures imposed on them by the Spaniards. At the yellow church, people were preparing for a peregrinación (walking pilgrimage) to Salta located 317 km (almost 200 miles) away.

There are a vast number of archeological sites in the Quebrada de Humahuaca and in the surrounding landscape. People first arrived here about 10,000 years ago and the area appears to have been continually occupied since then. Most of the history is pre-Inca, as the Incas had only expanded their empire to include this area a short time before the Spanish arrived (yet another conquerer).

Victor took us to a site with a large number of petroglyphs with a variety of ages. Some were formed in the past 600 years because they show the conquistadores on horseback. Others were much older. This petroglyph has llamas and ostrich-like birds called ñanus.

This region of Argentina is unlike any other in this country. Many traditional foods, music, and other cultural traditions are still followed. In many ways, it feels more like being in Peru or Bolivia than in Argentina.

This dish, called locro, consists of meat (often llama) with some combination of vegetables, legumes, and potatoes. As the place of origin for potatoes, there are many different varieties, most much smaller than the typical “Idaho potato”. Quínoa is also used in many dishes.

La Quebrada de Humahuaca—colorful landscape in NW Argentina

A quebrada is a valley or canyon formed by the action of flowing water. The Quebrada de Humahuaca is located in the northwesternmost corner of Argentina, on the eastern side of the Andes, where active uplift of the land has caused rivers to cut down and create quebradas of many sizes and shapes, resulting in a stunning landscapes of shear cliffs and massive incisions. 

This view to the west is down an east–west-oriented tributary quebrada near the town of Tilcara that feeds into the much larger Quebrada de Humahuaca that extends north–south. We went trekking with llamas (www.caravanadellamas.com), who carried our gear. My llama was named Puca, which is the indigenous word for reddish color.

The Quebrada de Humahuaca is an attraction for tourists because of its brightly colored rocks, which have been exposed as the Andes have been uplifted and rivers have cut down to expose rocks that range in age from Precambrian to very recent. The older rocks that have been somewhat metamorphosed generally have dark colors of greens and greys. In contrast, there are white and light grey limestones that formed from a variety of organisms in shallow marine environments. But what most catches the eye are the reds, oranges, purples and yellows of sedimentary rocks that were deposited in continental environments such as rivers, where exposure to the atmosphere caused iron in the sediment to oxidize (to rust!).

Pumamarca is a small town in the quebrada that is popular for its Cerro de Siete Colores (hill of seven colors). Of course, the number of colors is highly subjective!

On our three-day trip with the llamas , we were able to trek into the mountains east of Tilcara, to a much higher valley that is oriented parallel to the Quebrada de Humahuaca, which at Tilcara is at an elevation of 2500 meters (about 8000 feet). The scale of this vast landscape is impossible to capture in a photo.

Here are Jay and Adela, our guide, in the high valley near the house of Adela’s father, where we stayed over night. His house is located at about 3100 meters (10,000 feet). There are no roads and at an age of 78 her father lives without electricity or running water and must walk or ride his burro to town for supplies. 

These north–south valleys are all formed from east–west-oriented compression and are a series of folds (imagine pushing on a rug until it is folded into hills and valleys). We trekked around the high valley that is a large-scale syncline; that is, layers are inclined toward the center of the valley, although there are many complications to this overall structure.


We were able to see many small-scale features such as this syncline. Cactus for scale is about 2 meters (6.5 feet) high. The larger-scale features are more easily seen from the air or using Google Earth. 

A popular place to visit is the Serrania de Hornacal, located east of the town of Humahuaca. People go to the Mirador de 14 Colores (viewpoint of 14 colors) to see colors best displayed before the sun is getting ready to set. You can imagine that many photographers come to this part of the world and take great pains to be in the right place for the perfect exposure of colors in the early morning or late afternoon light.

This photo of the Serrania de Hornacal was taken in the late afternoon, but unfortunately rare spring clouds appeared to obscure the sun just before we arrived at the mirador. Nevertheless, it was a thrilling sight, especially because for geologists this is one of the finest possible examples of flat irons in the landscape. Flat irons are formed when layers (usually sedimentary) are inclined steeply and then eroded into shapes that look like the bottom of the tool used to iron clothes. The colors are a result of the different sedimentary layers that are exposed by erosion when water flows down the slope.

But only when I looked at Google Earth did I realize this cliff of tilted sedimentary layers is part of a large-scale plunging synclinal fold. All of the layers are tilted toward the center of the fold (we were viewing the north limb); in contrast, in anticlines all of the layers are tiled away from the center.

The reason for all of these folds will be explored in a future post.