Into the Great Unknown: Looking for the Rivers Within the Rivers of Marble Canyon

The Grand Canyon has many moods. So many of my pictures show a canyon bathed in bright sunlight and vivid colors, but twilight often revealed softer tones. The picture above is the view from my campsite at Buck Farm Creek at dusk on the third night of the trip.

We continued our journey into the Great Unknown of the Colorado River. On day four we were expecting to make for Nankoweap Creek about 11 miles downstream. For me it was the chance to find the "river" within the river. That's not some kind of philosophical quest. It was a geological thing, to be explained shortly. But before that, we did some exploring with the extra time afforded by a short distance on the river.

As we often did, we explored the area around our camp while taking advantage of the shade. We headed up Buck Farm Canyon just to see what could be seen. There were a lot of large fallen boulders of Redwall Limestone littering the lower slopes.

Buck Farm quickly narrowed as we climbed up the canyon. We had reached deeper into the crust and were now walking on ledges of Muav Limestone, which in most places underlies the Redwall Limestone. It seems simple to say that one layer sits on top of another, but there is just a bit of time difference between the two layers: the Muav dates from the late Cambrian Period, while the Redwall is Mississippian in age. More than 150 million years elapsed between the deposition of the two layers. That's the same time period that separates the Jurassic (and her many dinosaurs) and our own current era. What happened here?

We climbed over the dry talus slopes and eventually discovered a verdant canyon and even a small clear trickling stream. It was a nice little explore, but now the sun was shining down on us, furiously hot. We headed back to the river.

It was another day remarkably free of large rapids, with only President Harding Rapid (4) standing in our way. As we drifted down the river, more gigantic caverns could be seen in the Redwall cliffs. I think the alcove below is called the Royal Arches.

We also continued to see evidence of recent mass wasting activity along the river. The rockfall seen in the picture below shows a truer color of the Redwall Limestone. It's gray on fresh surfaces, but is often stained by iron oxides leaching out of the overlying Supai Group.

Mile 43 revealed an odd sight. A thousand years ago, the Ancestral Puebloans constructed a foot bridge across ledges of Muav Limestone. From river level we could see no sign of a trail or possible route on either side of the bridge, but there it was. We joked that it was a ruse designed to catch their enemies. They would climb up there to see where it went, where they could be picked off at random.

Some of the Cambrian layers in the Grand Canyon are greenish in color, especially the Bright Angel Shale. The color comes from a mineral called glauconite. The Bright Angel is composed of what used to be ocean-floor muds, and generally forms slopes. Where freshly carved by the river, it formed the ledges seen below.

At Mile 47, we reached Saddle Canyon. I kind of awoke from my entrancement and prepared to stroll up the gentle tributary valley. I asked about the cut in talus slopes to the left of the canyon. "Oh, that's the trail" they said, "the canyon itself is far too steep to go climbing in". Oh geesh, this wasn't going to be at all that easy! We started climbing the incredibly steep talus slope, up through several hundred feet of Bright Angel and Muav layers. It...was...hot.

 As always, though, the view of the river was wonderful.

 The "trail" leveled briefly. It was wonderful not stepping up and over the large boulders.

The stream valley rose to meet the trail, and suddenly we were in a merry little paradise. It's amazing what a little bit of water in the desert can do. Life was everywhere.

We reached the small waterfall and the lusciously cool pool at the base. My picture doesn't have people in it, but I can assure you that every one of us submerged ourselves under the water.

At this time of year I didn't expect to find many flowers, but in the cool moist micro-climate of Saddle Canyon there were some beautiful columbines, one of my favorite flowers.

 I spoke of a river within a river in the title. I was looking for something I had never seen before: the Temple Butte Formation. The Temple Butte is Devonian in age, around 400 million years, which puts the formation between the overlying Redwall and the underlying Muav Limestone. But it isn't a continuous layer. The Muav Limestone was exposed to erosion and eventually developed a series of river channels that ultimately filled with limestone as sea level rose in Devonian time. In other areas, the limestone covered the whole landscape, but after its deposition, the Temple Butte in eastern Grand Canyon was eroded again, leaving only lenses of the formation in the 400 million year old river channels. There are ancient rivers in the depths of the modern river canyon.

Walking out of Saddle Canyon, I spied a really nice example of the purplish Temple Butte between the Redwall and the Muav. If you can't quite visualize what I've been describing, I annotated the picture below. I missed the formation on my previous trips in the canyon, but once I saw it and knew what I was seeing, I began seeing it everywhere!

We continued to float down the river for four miles to our camp at Little Nankoweap Creek. The canyon was beautiful beyond words. Pete let me row again, and I even traversed two gigantic rapids. Okay, they were riffles. Okay, they weren't even that...they were piffles. But I did manage to navigate the raft into camp!

Into the Great Unknown: Exploring 300 Million-Year-Old- and 50 Year-Old Caves (and a bit of fossil hunting)

What the heck? Read on to solve this little mystery..

Our adventure in the Great Unknown of the Colorado River continued through Marble Canyon. We started the day with stops at Vasey's Paradise and Redwall Cavern (in the previous post) and now we were floating down a canyon with 500 foot sheer walls. Here and there, water trickled from springs in the Redwall Limestone, and at several of them seeds had found a place to root (below).

About two miles below Redwall Cavern we made a stop at another well-visited site: Nautiloid Canyon. Nautiloids were relatives of the octopods, and can be thought of as octopi with shells, some of which were coiled like a snail, or straight, like a long thin cone. Three species exist today, including the chambered nautilus, a common sight in curio shops. At times the nautiloids dominated the seas, especially during the Mesozoic Era (the "age of dinosaurs"). In Nautiloid Canyon, a number of them have been exposed by the erosion and polishing of the Redwall Limestone.

To see them, we needed to climb 75 feet up a limestone ledge and head into a slot canyon. They are easier to see when wet, so one of the party can be seen hauling a bucket up the rocks.

Before heading into the narrows, I stopped and took a look at the canyon below us. I wondered, here on the third day of our trip, if I would get tired of being inside these canyon walls at some point in the next thirteen days (for the record I never did!).

Marble Canyon is sometimes thought of as a sort of preliminary introduction to the "real" Grand Canyon. I found it to be one of the most beautiful canyons I had ever laid eyes on.

The nautiloids were quite fun to see (a two foot long shell is just left of center in the picture below), but in searching for shade, I noticed something else that I found very interesting.

 As I've mentioned before, the Redwall Limestone is riddled with caverns. Looking at the waterfaull that blocked any further progress up the canyon, I noticed there was a large cavern opening in the shade on the left. I walked up to see if it contained any of the usual cave decorations like stalactities or stalagmites (these features are collectively called speleothems).

What I found in the openings above my head was a surprise: there was a lot of red dirt and debris. It wasn't much to look at, but it contained the beginnings of an answer to a question I've asked myself on occasion. Could a cavern exist for millions upon millions of years in the Earth's crust? Many of the caverns that exist in the world today are a few million years old at most, but I understood that the Redwall Limestone exhibited evidence of karst topography, the sinkholes and blind channels that develop as caves grow and collapse. The karst developed not long after the Redwall was deposited in Mississippian time.

The sinkholes and caves would fill with debris from above, some being carried by rivers and streams. A new formation was described in the 1970s, nearly a century after one would think all the formations had been discovered. Appropriately known as the Surprise Canyon Formation, it is composed of stream gravels and silt layers deposited within the karst openings of the Redwall in late Mississippian and early Pennsylvanian time. It was looking more and more like I was finally standing in the opening of a cave that existed before the age of the dinosaurs! It had been protected through the ages by the fill of dirt and gravel.

Now, about that weird looking feature in the opening photograph. We stopped for lunch at mile 35.3 and I was directed to have a look at these miniature "hoodoos" (or maybe it was the maw of tourist-eating space creature). It didn't take long to see what was happening.

They were pools in the loose sand below springs dripping out of the ferns up above.

After lunch, we continued a few more miles down the canyon, drifting in the gentle current and enjoying the view of the high canyon walls. Caves were everywhere.

 We ran the one moderate rapid, Thirtysix Mile (4), without incident...

 A mile or two later we stopped at one of the most ominous sights I had yet seen. In the 1950s, a dam was proposed to be built in Marble Canyon. They went so far as to drill exploratory tunnels to test the soundness of the limestone. I was appalled that anyone thought to dam this river, and as a geologist I really wondered at the sanity of trying to plug all the holes in the cavern-riddled Redwall Limestone. The reservoir would probably have leaked like a bathtub with dozens of drains.

We stopped and explored the tunnels. I didn't take a camera, but I was surprised at the length (and complexity) of the tunnels. In the greatest depths there were hundreds of stalactites growing from the cave ceiling. New flowstone was draped on the tunnel walls like white icing on the side of a cake. The new speleothems were pearly white, and the stalactities were about an inch long. I was witnessing the formation of a brand new cavern after exploring another that has existed for geological eras. It was a strange juxtaposition, and the tunnels a jarring contrast to the magic of the river. What insanity would allow a dam to be built here?

The last few miles to camp remain in my mind as some of the most pleasant moments of the entire journey. We floated down a calm river, and after a bit, Pete stopped rowing and leaned back. We drifted with the current, and after the brief sound of water dripping from the oars, it was silent. Shadows had fallen across the river and the high cliffs were reflected off the surface of the water.

It was one of the most beautiful moments I could imagine.

Into the Great Unknown: Visions of Paradise, and a Bug's Horror

The third day of our journey down the Colorado River began as an idyllic journey through paradise. If that seems like a set-up for a disaster at the end of the day, it isn't, unless you count the poor bug (read below). We were traveling about 12 miles from Shinumo Wash to Lower Buck Farm Camp, a stretch of river remarkably free of large rapids (Thirtysix Mile Rapid, a 4, was about it). We were well into Marble Canyon, where the river walls are dominated by the Redwall Limestone (not really marble, but the river polish makes it look like marble). To me, the day was as close as I can imagine to being an earthly paradise: full of beauty, color and serenity.

The Redwall Limestone had its origin in a sort of serenity, or maybe stability is the better word. For millions of years during the Mississippian Period, between about 360 and 323 million years ago, a shallow tropical sea spread and regressed across the continental interior. The tropical waters were filled with life, including crinoids (sea lilies), brachiopods, bryozoans, clams, snails, fish, sharks, and even a few trilobites. It accumulated to depths of 400 to 800 feet, and the hard limestone forms one of the most prominent cliffs in the Grand Canyon (the location of practically every trail in Grand Canyon is determined by where it can cross the Redwall).

Limestone dissolves in mildly acidic water, so caverns will form readily in the Redwall. A vast network of caves are present throughout the Redwall, and many open out into the cliffs above the river. Being an armchair spelunker, I wanted to get out and find a way to explore every cave we saw in the cliffs above. Most were clearly inaccessible, but the cave in the photo above could be reached by humans. It was used by Robert Brewster Stanton in 1889 to stow some of their gear as they abandoned their tragic journey down the river after their leader (and bankroller) and two others drowned. It is called Stanton's Cave to this day.

It turns out, though, that humans have used the cave for a long time. 3,000 to 4,000 years ago, humans constructed split twig figurines, and left them in Stanton's Cave by the dozens. It is thought that 165 of these precious archaeological treasures were removed by visitors between 1934 and 1969 before the park service removed the remaining 74 during an excavation (my feelings about this looting is unmentionable in this family-rated blog).

Split twig figurines on display at Tusayan Ruins, South Rim of Grand Canyon National Park

Other creatures used the cave as well, including California Condors and Mountain Goats, whose dated remains go back 12,000 years. And remarkably, driftwood was carried into the cave during a river flood around 40,000 years ago. The cave is 160 feet above the river!

Most recently, the cave has been occupied by several species of bats, including the rare Townsends big-eared bat. The largest nesting colony known in Arizona was present here years ago, but persistent tourist incursions drove them away. Eventually a gate was constructed to allow access for the bats, but to keep people out. Apparently it has been working, and a colony has been re-established.

Just downstream of Stanton's Cave, an expected splash of greenery coated the slopes of the canyon before us. As we drew closer, we could see water bursting out of the cliffs. Water is another wonderful property of the Redwall. The caverns, fractures, and fissures provide avenues for groundwater percolating through the layers above to be concentrated near the base of the formation, and springs are a common feature at the base of Redwall Formation. Vasey's Paradise was a wondrous example of one of these springs.

We pulled out to have a closer look (for some it was an opportunity to fill their solar showers with clear spring water). We had to step carefully, because some of the greenery was composed of poison ivy!

I caught a shot of my brother enjoying a view from a large boulder along the shoreline. I carefully made my way down to join him. Carefully, because only a week before the trip I had done something to my heel and even had to use a cane for a day or two to get around. I didn't want a recurrence, and was only wearing sandals while on the river. The rock provided a nice upstream perspective of the springs.

Back on the river, we passed another Blue Heron. I couldn't resist another few pictures!

After another few bends in the river, I got a lesson in perceived scale. One can see a dark cavern at river level in the distance. As we got closer the hole got bigger...and bigger...and bigger! We had reached Redwall Cavern, one of the more extraordinary sights on an extraordinary river. John Wesley Powell remarked in 1869 that the huge declivity could hold fifty thousand people. Others later suggested more like 5,000, but in any case, it is huge. We pulled out for a little exploration.

Even before turning my camera into the cavern itself, I had to snap a shot or two of the reflections of the surrounding cliffs on the river. This was one of the calmest parts of the river so far, but Redwall Cavern must exist in part because of lateral erosion of the river during high water (the entire cave was filled with water in 1957 during a flow of 122,000 cubic feet per second; today's flow was more like 12,000 cfs).

Blocks of Redwall that had fallen into the cave contained numerous fossils. Some of our travelers pointed out the crinoids and brachiopods seen below.

I started exploring the depths of the cavern, taking the surprisingly long walk around the back of declivity. The scale is impressive, compared to the rafts of our little flotilla.

The ceiling of the cavern provides a nice frame for looking at the river.

Did I mention that the cavern is huge?

It was a fascinating place to wander, and a cool respite from the sun. I've also seen video of Redwall Cavern in an entirely different circumstance; check out this example of the cavern during an intense monsoon storm. It's awe-inspiring...

Ichnology is the study of trace fossils, the tracks, burrows and other traces of past life in the absence of shells or bone. I've seen many trackways in ancient sandstone formations, but we saw a bit of drama reflected in the sand within the depths of Redwall Cavern. A large beetle had been walking along the uneven sandy surface, and had come to grief in someone's footprint. Such dramas have been preserved in formations like the Coconino or Supai, and in the right conditions, the same could have happened here. The story has a happy ending; the beetle wasn't dead yet, and we set him upright again to continue his journey.

The day continued, but this post is already long. To be continued!

Into the Great Unknown: Whodunnit? A Mountain Range Goes Missing

The new day, our second on the grand river, began with a startling sunrise. Sunrises and sunsets in the Grand Canyon are not like other places. One never sees the sun rise above or dip below the horizon, because in the deep canyons, there is no such thing as a horizon. Like Plato's cave, we can only comprehend the sun rising over the Earth's horizon by imagining it from the reflections coming off the adjacent cliffs. If the sun hits camp at sunrise or sunset, someone has made a big miscalculation in choosing a campsite. Staying out of the sun for as long as possible is a continuing strategy during a summer rafting trip on the Colorado.

There was a foreshadowing of today's mystery in the previous post. On our continuing journey into the Great Unknown, rafting the Colorado River through the Grand Canyon, we had passed through three geological formations, the Kaibab, the Toroweap, and Coconino. The first two formed in a coastal environment, while the Coconino developed in a sand dune dominated desert. But we ended our first day on the river in the midst of the Hermit Formation, a striking red-brown layer composed of siltstone and mudstone. The bright red color in such rocks (and the presence of sedimentary structures like ripplemarks) is strongly indicative of deposition in a river floodplain environment.

As we drew deeper into the canyon, we encountered successively older rocks, and they revealed more and more redbeds. Now there were ledges and cliffs of sandstone and other coarser sediments, indicative of a higher energy environment, such as the river channels of large floodplains and desert sand dunes. Clearly a major geologic event had taken place, one that produced a vast volume of sediments over a wide region. For a region of the Earth's crust that had remained remarkably stable for nearly a billion years, this event stood out.

We had entered the Supai Gorge, named for the four formations of the Pennsylvanian-Permian aged Supai Group. Their names are tongue-twisters: the Watahomigi, Manakacha, and Wescogame formations and the Esplanade Sandstone. Where did all these sediments come from, and how do we know? The sediments had to come from a mountain range, but any such mountain ranges no longer exist, having been eroded to rubble many millions of years ago.

Ripplemarks and crossbedding in the sediments show that the rivers were flowing in a general southwest (today's southwest, anyway) direction, meaning the mountains lay to the east or northeast. In southwest Colorado, there are younger rocks, similar to the Mesozoic rocks found around Zion and Capitol Reef in southern Utah. But beneath them where the Paleozoic rocks should be found, there are only ancient Proterozoic metamorphic rocks and intruded granites. These ancient rocks are the roots of the Uncompahgre Uplift, otherwise known as the Ancestral Rocky Mountains.

The origin of the Ancestral Rockies remains somewhat of an enigma to geologists. They coincide in time with the collision of South America and Africa with the southeastern part of North America, an event that ultimately produced the supercontinent Pangea. But the Ancestral Rockies are hundreds of miles removed from the collision zone, so geologists infer a sort of chain reaction in the crust along ancient fault systems. In any case, the rise and destruction of a mountain range in Pennsylvanian and Permian time has provided us today with one of the most scenic and colorful layers in the Grand Canyon.

I came to love two bird species who make their home in the canyon. One of them was the blue heron. We would see them all through the canyon, gracefully soaring over the water, or stepping carefully in the shallows, looking for fish and other prey.

We continued to descend deeper into the canyon. Today's route would take us through a part of the canyon called the "Roaring Twenties", a series of rapids spaced on average only a half mile apart. After the relative paucity of rapids on the previous day, it was a real roller coaster. Remembering the scale of 1 to 10 for rapids in the Grand Canyon, we faced House Rock Rapid (7), North Canyon Rapid (5), Twentyone Mile Rapid (5), Twentythree Mile Rapid (4), Twentythree and One-Half Rapid (4), Georgie Rapid (6), Twentyfour and One-Half Rapid (6), Twentyfive Mile Rapid (6), Cave Springs Rapid (5), Tiger Wash Rapid (5), and Twentynine Mile Rapid (2).

All the boats made it through the rapids without incident, until (I think) Tiger Wash. As we slipped over the tongue of the rapid, I thought I saw one of the boats go vertical, and someone tumbled out. I thought it was my nephew at first, but soon found that it was the boat with my brother and his wife. Somehow they had stayed in the boat, but unbeknownst to them, their oarsman was missing. They heard him say something along the lines of "your oarsman is NOT in the boat". They looked behind in surprise as he clawed his way back onto the raft just in time to get hung up on a boulder. Our raft was closest, so Pete rowed back into the eddy, and we started to climb up the rocks to see if we could assist, but they managed to back off the rock, and we were able to continue on.

Looking up the canyon, we could see that the monsoon storms were not finished. The towering cumulus clouds were wreaking havoc upstream, but the day remained sunny and clear for us. Tonight I would be sleeping under the stars.

We passed another stunning example of mass wasting just before hitting the Roaring Twenties. Boulder Narrows is a huge single chunk of Esplanade Sandstone that practically dams the river (below). According to the river guide, it is the single largest boulder to be found in the river through the Grand Canyon.

The canyon became deeper and more vertical.

At lunch, I was able to concentrate on smaller things, like the wonderfully colored and patterned river boulders.

The Supai Group is one of the thickest units in the Grand Canyon sequence at more than a thousand feet, so it was with us for quite a few miles. I had not been this close to the redbeds in a long time, and the ledges and cliffs made for a scenic stretch along the river. The combination of scenery, geology and rapids made for a memorable day.

There was an otherworldly appearance to the cliffs that rose above us, straight out of the river.

At mile 23, a new layer appeared, hard ledges of gray limestone. We had reached the Mississippian-aged Redwall Limestone. There wasn't a bit of red in it, at first, but that would change before long. I'll save the detailed description for the next post, because today's exposures were just a preliminary tease.

The Redwall Limestone is a true cliff-forming rock, and in places the rock hung over the river.

After the excitement of eleven major rapids and a near miss in the flip department, Pete was a bit tired. We were past the rapids of the Roaring Twenties, so I took to the oars for a couple of miles. I'm not saying I'm a natural oarsman, but the several miles I rowed probably amounted to about a half mile of actual river. I had a devil of a time sticking with the current and staying out of the eddies. Plus, you can see I didn't put on my gloves, so I also got a blister (whine, whine). It was fun!

In the next post: the incredible Redwall Limestone of Marble Canyon.