Wednesday, August 21, 2013

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!

1 comment:

Anonymous said...

Beautiful photos thoughts and information!
- Richard Anderson