The Mojave National Preserve - A Geologic Paradise

When some people hear the word Mojave, they may think of snakes, centipedes, or spiders. Maybe even cactus, sand, and desolation. But lovers of the Mojave well know its charms, perhaps more difficult to discern in July but here nevertheless. In March, I traveled to the Mojave National Preserve with 11 former students to learn about this varied landscape. What we found more than anything else was the unexpected. Sand yes, but snow too. Cactus and other desert vegetation but all growing next to some pretty fantastic rocks. The weather was challenging but all good things have a rightful price.

We entered the Preserve on the south at Essex Rd. The preserve was created in 1994 to help stop the wanton destruction of this lush desert locale.

Our first stop was at Hole-in-the-Wall, located to the east of the Providence Mountains.  Pyroclastic rocks are exposed here and have weathering into fantastic shapes.
 

We followed a trail into a slot canyon that has been carved during the numerous summer thunderstorms that rack this landscape. The rocks are mostly resistant but cannot withstand the hard boulders washed through here.

A set of ring bolts helps hikers negotiate the steep drop-offs. The trail was bout one mile in length and we got an appreciation for the power of explosive volcanism.

At Hole-in-the-Wall, tafoni textures permeate the rocks. These features begin to form long before the rock is exposed to erosion. Groundwater moves through the ash flow and can dissolve some of the silica. No hole is created at this time - only pockets of weakened rock. Some of the dissolutioned silica is redeposited adjacent to the weakened areas. When the rock is exposed to erosion, the weakened areas form holes while areas with extra silica cement surround them!

 

Taking a break along the trail. The banded range in the distance is the Woods Mountains and is the center of this explosive volcanic complex. It erupted 18.5 million years ago, making is the same age as the famous Peach Springs Tuff in Arizona. Neither the Mojave nor the Basin and Range were in existence at this time. Rather Woods Mountains Volcanic Complex is one of the last vestiges of the Mogollon Highlands which stood here.

Volcanic stratigraphy exposed near the Hole-in-the-Wall Visitor Center.

During the first night's camp at 4,500 feet, it rained a lot. Thankfully, it did not start until we were snug in our sleeping bags, then let up just before sunrise - Camelot! As we poked our heads from out under the rain fly, this is what we saw - snow in the Mojave! We had come here in hopes of finding Spring, but winter still lurked in the air.

Just 500 vertical feet above us, there was snow that had accumulated to about 3 inches. We drove through this wonderland of volcanic rock and snow.

Pinto Mountain on the southern fring of the New York Mountains. Unfortunately, this meant that we could not visit, hike, and camp at Carruthers Canyon.

So instead we drove south to a lower elevation to hike the Kelso sand dunes. You can see them far off in the distance glowing in the sunshine.

A trail (of sorts) leads to the top of the dunes. I remember hearing in grade school that there were more stars in the universe than grains of sand. When you hike on a dune field like this, it seems almost unimaginable. And then we heard on this trip about a new book, "The Hidden Reality", by Brian Greene, that talks about parallel universes and the possibility that there are many other universes - some that may be just like this one. Sand dunes have a way of making everything seem big.

The sand comes from the Mojave River as it flows into Soda Lake north of here. As the river dries in it's bed, the wind picks up the loose sediment and blows it south towards the Granite and Providence mountains. These ranges create a barrier that slows the wind and the sand grains drop here on the desert floor. Look for pictures and a story about the Mojave River below.

Dark colored minerals such as mica, hornblende, and pyroxene are layered within the more common quartz grains. Settling and deformation of the laminae creates this unusual and striking pattern on some dune faces. In reality, all of the grains reflect the mineralogy of the San Bernardino Mountains, where the Mojave River originates. As it flows north from there, it picks up sediment from other ranges - the Rodman Mountains, Cady Mountains and so on. The sand that arrives at Kelso dunes is the eroded remains of these ranges, piled exquisitely into fashionable dunes.

The Providence Mountains lie east of the Kelso dunes and were laden with wet clouds on the first day of spring, March 21, 2011

The Granite Mountains to the south of Kelso dunes

From the top of the dunes, we could see our next destination on the north horizon, the famous Cima Dome.

We hiked 1.5 miles on the Teutonia Peak Trail to get this view of the Cima Dome from the east. Cima Dome originated as a giant mass of Mesozoic granite that was emplaced as hot magma deep in the crust. The granite was uplifted and exposed to chemical weathering, where the feldspar were degraded, causing the other mineral grains (quartz and mica) to become liberated. This chemical weathering was perhaps aided by fracturing and jointing. As the weathered debris was plucked from the mountains, it could not travel far in the dry desert and the reaming granite mass became buried in its own debris! The Cima Dome.

This is said to be the densest stand of Joshua trees in the world. And my friend and botanist Orlando Mistretta says it is a subspecies too, The Jaeger Joshua (Yucca brevifolia jaegeriana)

Joshua trees and the Ivanpah Mountain in snow.

Next on our geologic tour was a visit to the Cinder Cones and Lava Flow area in the Preserve. Basaltic volcanism occurred here between 7.5 million years ago and 8,000 years ago and left behind 33 craters and cones. Here Louise poses in front of a large volcanic bomb on the slopes of one of the cinder cones.

This is a fantastic area to explore and the scenery was fabulous. Another eruption is likely but no one knows when.

Our final day in the field saw us join up with Dr. Norman Meek of Cal State San Bernardino who showed us some wonderful Ice Age lake evidence in the Mojave. Here is a shingled beach deposit from the shore of Lake Manix.

And a view from this strand line to the west. All of the low ground where the interstate exists today was under lake water about 19,000 years ago.

Note the bed of the Mojave River flowing away from the photographer to the upper right. To the left of the river bed and slightly above it are green clays laid down in Lake Manix. The earth tone deposits on top of these (and in the left foreground) are delta sequences that prograded from the west onto the lake sediments. A glorious sequence indeed!

While standing on top of the delta sequence, we could look across old Lake Manix and see a wave cut terrace of the former lake etched into the north side of the Cady Mountains. Most folks probably don't think of "lakes" in the Mojave Desert, but the Ice Age climate was pluvial at this time.

Dr. Meek pointed out tufa deposits that line rocks along various shorelines of old Lake Manix. Such deposits are still found along the shore of Mono Lake north of here.

Students walking on a ridge towards Lake Manix deposits.

Three sequences can be seen from here in the walls of a side canyon to the Mojave River. The light colored deposits below are granite rich fan material that originated to from the north and were washed south (right) before the river was here. These are overlain by volcanic rich deposits (gray-purple beds just below the ridge top) that came from the Cady Mountains to the south of here. These in turn are overlain by the green lake beds of Lake Manix seen on the ridge top to the right. The source terrain for each fan sequence is still visible in the area and shows what was present in this valley before the lake developed.

Here we see a lake bed remnant on top of the fan sequences. The green color comes from reduction of the iron minerals in the deposit.

Dr. Meek shows evidence for the fluctuation of the lake shore. In the lighter colored bed behind his right hand is a course cross-bedded sand. The greener beds behind his left hand are finer grained clays. The interpretation is that when the lake shore dropped, sand was washed into the area, and as the lake expanded, the lake beds covered the area.

The Cady Mountains fan sequence (brown, irregular eroded beds below) topped with Lake Manix clay sediment (upper green beds). Afton Canyon can be seen in the backgound.

A marvelous sequence that would be entertaining even to non-geologists. Knowing the origin of the scenery just seems to add to the enjoyment of this special place.

Our next stop was up into Afton Canyon, along the track of history.

The Manix Fault rips through the canyon and has upended many of the once flat-lying rocks here. Rainwater then runs down the vertical bedding creating this interesting texture.

It almost reminds one of Bryce Canyon on a small scale.

Afton Canyon

Runoff has carved some spectacular slot canyons into the old alluvial fan sequences.

This canyon became so narrow, you literally needed a flashlight to see in it. Thank you to Dr. Meek for meeting with our group in the desert to share his expertise on Lake Manix and its history.

This is a long blog and I'll end it here with a picture of the Providence Mountains, looking southeast from the Cinder Cone area. It was great trip with challenging weather but the Mojave National Preserve is worth a visit. Bring a geologist with you!

Article Published on geology.com

My article "How Old Is The Grand Canyon?" went live this morning on the web at geology.com. You can jump right to it here. Thanks to Michael Conway of the Arizona Geological Survey for connecting me with Hobart King who operates the site.

The history of the Grand Canyon is large and complicated but there is nothing I enjoy more than making its story at least a bit more understandable and accessible to those not well versed in geo-speak. Hopefully, this article will do just that. Enjoy it and share with your friends.

Book Review: North Pole South Pole

I rarely do book reviews on this site, it being more oriented towards field explorations in the southwest. But I can not count how many times I have been leading a trip and someone asks me detailed questions about the earth's magnetic field. There is just something about the earth's magnetism that is ... well, magnetic to some folks. They want to know how it all works.

Maybe it's because all of us used to use magnets in the dirt as children to gather iron filings. That was cool. Or maybe it's the way a compass intrigues us - magnets always point north no matter where we go. (Although on my first trip to the South Pole in 1986, we pulled out a compass and watched the dial point down against the bottom of the compass as it tried to point north from there). The next time someone asks me about the earth's magnetism, I'll just tell them about Gillian Turner's new book, "North Pole South Pole", published by Awa Press (New Zealand) and The Experiment (New York). This small but handy book contains a history of our knowledge about magnetism, and the scientists who have studied it through a long span of time.

As most geologists will know, the earth's magnetic field sometimes switches such that what is now magnetic north reverses to the other side of the planet. This last happened about 780,000 years ago and many scientists wonder what a magnetic reversal would "look like" if we lived through one. Do species go extinct during these events or become confused when they migrate? How long do reversals last? Readers of this book have to wade through gobs of history concerning past study and understanding of the magnetic force to find these answers - the book deals mostly with a chronology of this understanding. I wish there would have been a table in the book where all of the "facts" concerning the magnetic force were readily available. As such, this is a book that will likely find favor only to other scientists and historians of science.

But I still found the reading worthwhile. Turner is a very easy-to-read writer who crafts her sentences well, with stories that flow nicely. Most of us received what little knowledge we have of the magnetic field in grade school and a book like this has such a depth of information about the important milestones in the field that you are sure to learn much from it. But you'd have to be interested in the topic in a big way to keep slogging through all of that history. Someone could probably write another book for non-scientists on this topic that would be more approachable, but if you are a scientist and want to know about the history of magnetic studies, this is your book.

I learned many things from Turner but the most fascinating was that the strength of the earth's magnetic field has dropped 15% in only the last 200 years. Could this suggest that a magnetic reversal is underway? Perhaps we will get a chance after all to live through one of these!

An East Africa Volcano Like No Other!

Many friends have been e-mailing me about this link from the Boston Globe. If you have not yet seen these pictures of a crater located along the East African Rift Valley, you must see them now. Follow the link here.

"Birth of the Grand Canyon" Airs on Nat Geo TV

Way back in June, 2010 when the World Cup was in full swing in South Africa, myself and other geologists were participating in interviews on the rim of the Grand Canyon with a film crew from National Geographic TV. The production is titled "Birth of the Grand Canyon" and made its debut February 24 on the Nat Geo television channel. I haven't seen it yet but many viewers tell me it was well done and clearly presented. You can view a short trailer of the film here.

Rebecca Flowers

Carol Hill

Featured in the production are colleagues Ron Blakey (paleomap creator), Carol Hill (karst researcher), Rebecca Flowers (thermochronologic researcher), Karl Karlstrom (field geologist), and many others including myself. It is nice to see the science of geology and the Grand Canyon displayed so prominently on the tube. I hope you'll be able to catch the show. It will be running many times through out the years. Check the natgeotv.com and search for Naked Science.

Searching the Origins of the Esplanade Platform in Grand Canyon

Far away from the main tourist areas in Grand Canyon lies a huge wilderness of stone and space. It is silent beyond belief and seldom visited. Within this huge expanse lies the Esplanade Platform, a stunning landscape feature that is found only in the central and western portions of the canyon. The Esplanade forms a broad terrace positioned about a fourth of the way down in the canyon, where the Hermit Formation overlies the Esplanade Sandstone. The Esplanade thus creates a canyon within a canyon. Geologists have long been intrigued by the presence of the Esplanade Platform in Grand Canyon and many theories have been proposed to explain its origin. Did the Colorado River carve it during a period of erosional quiescence, as some say? Or did it form in response to the canyon's variable stratigraphy? I explored these questions on a recent trip to the Esplanade. From February 10 to 16 I was privileged to backpack with two other friends here. This is our story.

The trailhead is located in the Grand Canyon. A poor road leads to the boundary of the Kanab Creek Wilderness, administered by the BLM. Here we parked our car to begin our journey. You can see tumbleweeds piled against the boundary fence of the wilderness area on the right side of this photo. We had no idea at this point what wonders awaited us.

This is the canyon we walked down to access the wilderness. The lower red slopes are cut into the Hermit Formation, a rock unit that plays an important role in the development of the Esplanade.

At the start of our hike we immediately became aware of the great space we would be experiencing on this trip. Usually a backpack into the Grand Canyon is a trip into the "womb of Mother Earth," with the high cliffs closing in tightly all around. But travel on the Esplanade is different. You can see far and the promenade makes for some exhilarating views.

But make no mistake about it - this is very far away from everything human. Any misstep or fall that would lead to an injury would require someone to backtrack out again many days walk to the trailhead, then to fetch help as quickly as possible. A trip out here is to place yourself in the hands of fate, come what may.

Here Frank R. walks up a slope in the Esplanade Sandstone. You can see the cross-bedding evident in the many shadowed lines. The Esplanade is the first deposit in the canyon of Permian age and was laid down in a dune field about 290 Ma (million years ago). I include a paleogeographic map of the Esplanade Ss. below to show the geography of the Grand Canyon region at this time.

Esplanade Sandstone time in the American Southwest at 290 Ma. Note the faint outlines of the Four Corner states in this image. The yellowish pattern denotes sand dunes in the ancient landscape and the small red line in northern Arizona represents the 55 miles that we walked in the seven days of backpacking.

Even though we had bright sunshine for all but the last day of our hike, ice was still present in the many side drainages we passed that never receive sun this time of the year. They formed some spectacular icefalls on the Esplanade.

Frank taking notes on the Esplanade with Jump Up Point visible in the far distance.

The Esplanade forms many beautiful overhangs and we walked past many of them in our seven days. Note the pile of gray rubble on the floor of this one, which signifies a place where ancestral people once roasted agave. Although it felt like we were the only people in all of Grand Canyon on this hike, evidence like this reminded us that we were not the first ones here.

Some of the overhangs were extreme and formed cave like entrances that framed the canyon beyond.

And we utilized many overhangs for sleeping, as the temperatures at night dropped into the 20's. Sleeping in an overhang could make a 10 degree difference on the warm side!

In this wilderness adventure, our only source of water was from potholes that had been replenished from the late December snow storms that swept across northern Arizona. We estimated that 90% of the potholes were already dry from the extremely dry conditions that persisted in January after these storms. We had to hunt occasionally for potholes with water.

So, what about the Esplanade? Why is there such a broad platform within the canyon at this level? Look at this view of the upper 1/4th of the canyon and note that the Hermit Formation is barely visible, being covered in talus or colluvium from above. This strongly suggests that it is erosional retreat of the Hermit Formation that undercuts the overlying rocks, causing them to collapse and bury the Hermit in the collapsed debris. Note the more recent rivulets that have been etched into this debris apron (center) and a lot more of this recent erosion into the apron on the far right side of the slope. We can imagine that the apron of debris was once more extensive and "smoother" across this view.

In this view you can also see what used to be a continuous apron of talus covering the Hermit Formation, until it was partially eroded by runoff off of the upper cliff. It is likely that the aprons of talus formed during the Ice Age (pre-10,000 years ago) when conditions were much wetter in northern Arizona and the American Southwest. The dissection and partial removal of the talus aprons most likely has commenced in the last 10,000 years. So another question presents itself - what drives the retreat of the Hermit Formation (and the generation of talus) and what causes the non-retreat of the Hermit Fm. and the partial destruction of the talus aprons?

First, the episodic nature of talus creation and removal can be seen in the many talus remnants that are perched today as isolated remnants on the Esplanade. Here, Bryan B. stands in front of one huge remnant which is seen in the middle distance as a whitish-capped surface that slopes to the right, well below the canyon rim. This isolated remnant of upper cliff material used to be connected to a talus slope that once covered the Hermit Fm., well before it was stripped back to its present position.

And here, I am standing in front of another smaller remnant in the right background. These old remnants definitely show that the creation of talus and its ultimate destruction is episodic in nature.

In modern Grand Canyon, many springs are developed at the contact between the red Hermit Fm. and overlying white Coconino Sandstone, marvelously visible here where the talus cone has been recently eroded. We can imagine that during the wetter conditions of the Ice Age, spring discharge was much greater at this contact. This increase in discharge is likely what caused the Hermit Fm. to retreat rather rapidly, and thus undercut the cliff above it, thereby causing the creation of an extensive talus apron. When the Ice Age ended, the springs dried up, the retreat of the Hermit Fm. was arrested, and the talus cones began to be eroded like we see in the photo above. Thus, the remnant talus deposits that are curiously scattered across the Esplanade may show the rather recent development of the Esplanade Platform. In my observations, the Colorado River in ancient times had nothing to do with forming the Esplanade, it developed "locally" through fits and starts during Ice Age glacials and the intervening interglacials.

Within the talus debris that litters the Esplanade, we observed many great fossils in boulders of the Kaibab Limestone. Here are some well preserved crinoids we found one day on our hike.

And here is a fossil sponge also preserved in the a block of the Kaibab.

Walking on the Esplanade. There was very little trail in this stretch of the hike and only well-experienced Grand Canyon hikers should attempt to enter these remote locations. The possibility to get lost or sustain an injury is great.

But the scenery was fantastic. Here Bryan and Frank ponder a rock sentinel.

Our route took on a platform that is extremely untraveled in the Grand Canyon, the top of the Redwall Limestone. This surface is not well-developed in most parts of the canyon and does not have a name at all like the Tonto or Esplanade platforms.

But we enjoyed this tramp across the surface of the huge Redwall cliff.

Back on top of the Esplanade, I noticed some well-developed channels that are cut into the Esplanade Sandstone and filled with deposits of the Hermit Formation. These channels would have been features on earth;s surface some 285 Ma, when the lower part of the Hermit was laid down across the lithified dunes of the Esplanade Sandstone.

Here is the same photo with some guides to show you these very subtle features. It is likely that the Esplanade Ss. was already a rock when the channel was cut into its top surface. Then fluvial mud was washed into the channel.

Here is a close-up of the same channel above.

And a look at one other channel I took a photo of. This one might be a bit easier to see to the untrained eye.

Our hike was a glorious success. No one was injured, we found water when and where we needed it, and we lucked out beating a huge snow storm that blew in just as we were leaving. But more than that, we experienced the Grand Canyon on a very personal level. Bryan and Frank were excellent backpacking companions and I am lucky to have friends so dear and willing to undertake such an adventure. Geology was also my constant companion on this hike and I cannot imagine not being aware of its overriding presence everywhere upon this landscape. If you would like to experience the marvels of the Esplanade Platform in Grand Canyon, you can take a much more accessible backpack on the South Bass Trail, or drive out to Toroweap Overlook on the North Rim.