From our camp at the junction of Tuckup and Cottonwood Canyons, we day-hiked up Cottonwood one afternoon. The lower part of the canyon involved a bit of scrambling and meandering around and through various jumbles of boulders. There were pools and trickles of water the whole way up. After a while we reached a pour-off with a couple of cottonwoods at the bottom, which we had to leave the canyon bottom to get around. The slope on the Northern side was loose and full of talus; we climbed it one at a time to avoid setting off a rockslide on each other.
Arizona Steve ascended first. As I followed, I could see that the sidehill placed us at the base of a second, higher pour-off that was recessed into an alcove, which Steve had already detoured into. As I paused scanning for a route on up, he called for me to come check it out. The alcove was fronted by a stand of small cottonwoods, behind which lay a pool backed by a wonderful hanging garden.
All About Hanging Gardens
Hanging gardens occur across the Colorado Plateau where continual seeps of water emerge from rock/cliff walls, creating little oases of moisture, and often shade, which support a community of plants quite different from the surrounding desert.
The reason for these seeps has to do with the hydrology of the rock layers. When you’re traveling across slickrock, it’s easy to see it as dry and waterless. In rainstorms water quickly runs off the rock surfaces (leading to flash flooding). What water does linger pools in pockets and potholes that generally dry up after a time*.
*That time of course varies by the size, depth and aspect of the pocket. Exceptionally large/deep pockets are known as “tanks” and are often year-round effective water sources.
But the rock layers are full of cracks and crevices, and some portion of rainwater trickles down into these hideaways, working its way downwards, leading to the creation of effective reservoirs or even modest aquifers within the rock. Where the crack/crevice network leads to a sidewall or cliff, the waters seep out in tickles or drips. The seep works slowly to weaken and break apart the structure of the wall underneath, causing just to break off and fall away, gradually forming an alcove.
Often this happens when the water encounters less permeable rock below, such as less fragmented/porous rock or a layer of shale, and is forced sideways. In canyon country a likely place for this to happen is at the interface of 2 distinct geologic layers. Further North in Southern Utah, this often happens where the Navajo and Kayenta formations meet. Down here in the Grand Canyon, those younger layers are nowhere to be seen, and so the Cottonwood Canyon alcove-garden, which is also a transition-layer garden, occurs among very different- and older- rock layers.
Extra Detail: Almost all hanging gardens in the Western US occur in/on sedimentary rock layers. And interestingly, some types of sedimentary rock are better “hosts” than others. Specifically layers like the Entrada and Navajo Formations, which have strong cross-bedding, which creates frequent, horizontal layers of increased impermeability, are common host formations. But Wingate- just a little below Navajo- has thinner, less clearly-defined cross-beds, and almost never hosts hanging gardens.
*For non-geology-minded Utah mountain bikers: Navajo is what you’re rolling across on Moab’s Slickrock Trail. Entrada is what you’re “surfing” up at Bartlett Wash. I did a geology-mtn biking post early this down around Gooseberry Mesa, but would love to do a broader mtb-geology post across Southern Utah. We’ll see.
When I learned this, I thought about my absolute favorite hanging garden, at the head of Twin Corral Box Canyon, which I will describe further on down in the post. Twin Corral Box, when you hike into it from the Dirty Devil, is walled with massive Wingate cliffs. But at its upper end, higher up, the cliffs are Navajo. Higher up-stream on the Dirty Devil BTW, the side canyons are overwhelmingly Navajo-walled, and as a result many of them, like the Robber’s Roost system, host wonderful hanging gardens all over the place. (One of the most rewarding things about this whole project has been the numerous ah-ha! moments when something I noticed years ago suddenly makes sense…)
Immediately above the garden is the bottom of the Redwall Formation, which we looked at in the last post. Our hike led us up through the Muav, but in between appeared a narrow and very different layer, which I believe was the Temple Butte Formation (and which I’ll describe later in the post.)
An alcove-hanging-garden- which is a specific type of hanging garden- supports an array of plants roughly divided into 3 zones. At the bottom of the alcove, by the base of the wall and often alongside a pool, are the most “normal” plants, by which I mean plants that root in soil and grow upwards. The soil is formed very gradually from fragments of the collapsing rock wall. Because the soil is limited and forms so slowly, alcove-gardens are fragile places. If the limited soil gets excessively trampled, peed/pooped in/on or otherwise abused, the plants community in this bottom layer can be disrupted or destroyed. (Exotics- like Tamarisk or Ravenna Grass, Saccharum ravennae, can also mess up this zone.)
The middle zone is the “wall” zone, up against the flat, damp, soil-less vertical rock wall of the alcove, and this zone supports mainly algae and cyanobacteria.
Most of the algae species that live on alcove walls are not endemic to that environment, meaning that most occur also in other environments. In a study in the late 1980s roughly 204 species of algae were found on Utah hanging garden walls, out of ~1,900 known statewide*. Of those 204, only 16 were not known to occur in any other environment than hanging gardens.
*I don’t know if this number has increased significantly since then.
But what is different about the algae in hanging gardens is the mix of species. Many are Chrysophytes, Golden Algae (pic right, not mine). The times we’ve looked at algae in this blog, we’ve generally been talking about Green Algae, which are sort of like really, really simple plants- either unicellular or multicellular- that have no specialized or differentiated cells.
Like Green Algae, Golden Algae are generally teeny-tiny photosynthetic creatures, but they’re not at all closely-related to them. In fact they’re likely about as distantly-related to Green Algae as we are. The systematics of these guys are still unsettled (and the group itself appears to be polyphyletic), but it now appears that they belong to a completely separate kingdom, the Chromists, Chromista*, which includes Brown Algae, Yellow-Green Algae and Diatoms, in addition to a few other things you never heard of.
*Way unsettled. In the 2005, an alternative kingdom, Chromolveolata, was proposed, and then in 2008 it was proposed that this group be split into 2 kingdoms. I can’t keep up. In any case, they’re way, way different from Green Algae, and they’re most certainly not plants.
Tangent: This is what is so cool about life at the microscopic level. Up here on the giganto-macro level where we reside, we perceive only a little fraction of the diversity of living things. The “kingdoms” or “kinds of living things that we can see and touch- animals, plants and fungi- appear to be just 3 of 6, 7, or maybe 11(?) kingdoms of eukaryotic creatures. And then of course there are the kazillions of prokaryotes…
Most of the time, most Golden Algae species behave more or less like Green Algae- sitting around, mostly in damp/wet places, and photosynthesizing. But here’s something cool about many of them: when deprived of light, or when they find themselves in the presence of abundant alternative food, they can switch to a predatory mode, feeding upon bacteria and diatoms. Golden Algae are sort of like little alternate-universe plants that can turn suddenly and opportunistically carnivorous.
Chrysophytes are common in fresh water, and important in lakes, where they’re believed to be a main source of food for zooplankton. Hanging garden walls seem to be a good environment for them: Roughly half of the 1,900 known algal species in Utah are Golden Algae, but they account for about 70% of the species on hanging garden walls. There’s more happening on those slimy walls than meets the eye.
But the most interesting and eye-catching plants occur in the uppermost zone, at the top of the wall or on the “ceiling” of the overhang, rooted directly on or right by the seep itself. Small bits of soil do form and accumulate here, providing nutrients and helping plants to root/attach. But oftentimes the substrate in this uppermost zone is neither bare rock nor soil, but tufa, specifically calcareous tufa. Tufa is a type of porous limestone created by water depositing carbonate minerals. A very dramatic example of tufa is the huge columns ringing Mono Lake in California. Calcareous tufa, the type found in desert seep-alcoves, is a type of freshwater-deposited tufa with a specific laminate structure and is less porous than most tufa types. Tufa of all types can contain lots of organic matter from debris trapped in its formation. In alcove hanging gardens calcareous tufa often forms a thin, flaking layer on the “ceiling” and sloping upper walls of the alcove.
The common plant at the seep zone is Maidenhair Fern, genus = Adantium. There are more than 200 species of Adantium ferns* worldwide, many of which have adapted to rock walls, seeps and waterfalls. Our species here on the Colorado Plateau is Adantium capillus-veneris, known alternately as Black Maidenhair or Venus-Hair Fern (pics left and above right). A. capillus-veneris has atypical, sort of “un-ferny”-looking fronds, which look almost like little Gingko leaves. They root well on calcareous tufa, and form thick, lush, bright green, hanging “mats” within the alcoves, decorating the upper walls like draperies.
*I covered the basics of Ferns, and their freaky-cool haploid-diploid generational pattern last year down in Costa Rica. Man, it is like I have a post for everything.
Another seep-zone plant was in flower. When it first caught my eye I thought it some type of Gilia, but it was actually Scarlet Lobelia, Lobelia cardinalis (pic right*). Lobelia belongs to the Bellflower family, Campanulaceae, and probably the most closely-related thing to it we’ve looked at previously was Harebell last summer up in Glacier NP. Scarlet Lobelia favors moist environments such as stream banks, bogs and meadows in addition to alcoves. Its red, deep and narrow-tubed flowers are pollinated by Ruby-Throated Hummingbirds (like Gila). It was used medicinally by Indians to treat bronchial ailments (including asthma) and supposedly syphilis.
*Sorry- for some reason I only snapped this one rather low-quality shot. I have no excuse except that I take lots of photos when I hike, and don’t really know at the time what- if anything- I’ll blog about.
Tangent: I say “supposedly” because I can’t count how many plants I’ve read about that Indians allegedly used to treat syphilis. Seriously, it has to be dozens. What I wonder is whether any of these plants actually eased the symptoms of the disease (certainly none of them cured it) or whether the Indians were just so desperate that they pretty much tried anything. And in fairness, Syphilis appears to have been a much more virulent (and horrible) disease during its first recorded few decades in Europe than it was by the later 16th century, by which time it was basically the disease it is today.
Syphilis BTW has a fascinating and still unsettled history. For a long time, it was cited as a classic example of a New World disease spreading to the Old World. But other researchers believe that it was already present in both New and Old Worlds. Still other researchers hypothesize that it evolved in the Old World, was carried across the Beringian land-bridge with Paleo-Indians, and then re-encountered by European explorer. The timing of the disease’s history in Europe is tricky; the first major outbreak was in 1494, which would mean that if it was a New World pathogen, it pretty much would have had to arrive in Europe via Columbus’ first voyage.
Nested Tangent: I sometimes pick up a tone of explanation or justification in traditional New-World-Origin accounts of Syphilis. Yes, we gave the Indians Smallpox and a whole bunch of other diseases, the story goes, but hey, they gave us syphilis, as though it somehow balances things out.
Today in the age of AIDS, syphilis is farther down on the list of most folks’ STD-worries, yet another of the multitude of terrible diseases that’s largely been beaten in the First World, allowing so many more of us to live long enough to succumb to cancer. I wonder, if they ever cure cancer, what we will start dying of next?*
*I’m reminded of the old Red Foxx line (paraphrasing): “All these health nuts are going to feel stupid someday, lying in a hospital bed, dying of nothing.”
Scarlet Lobelia’s medicinal properties- whatever they are- likely are a result of the plant’s alkaloids, which can be toxic, and probably shouldn’t be messed with. BTW, you won’t find this flower in hanging gardens up around Moab or Canyonlands; though it’s common in them around the Grand Canyon, Glen Canyon NRA and Zion, it doesn’t appear in hanging gardens further North.
Alcove hanging gardens always seem quiet, contemplative places. When I’m in one I always feel as though I should speak softly and be respectful somehow. I don’t know that this feeling stems from any karmic-greenie Earth-vine or anything, so much as they half-consciously remind me of cathedrals, with their dim light, still, cool air and vaulted ceilings. The Cotton Canyon Alcove is small- maybe 30 feet high, but I’ve stood in others that are huge. The side canyons of the Dirty Devil in particular contain a number of spectacular ones, the largest and most amazing of which lies at the head of Twin Corral Box Canyon, with a ceiling of well over 100 feet high.
Alcove-gardens are cool, refreshing places offering a break from the sun and heat of the surrounding desert. In the really large ones, the cool, damp air can induce a deep chill within 15 minutes or so, driving you to fumble around in your pack for an extra layer, or retreat back into the sun. Our small alcove was just perfect though, and we found ourselves lingering for a bit. These places have an out-of-time feel to them; it’s easy to be surprised at how much time you’ve dawdled away if you get distracted or don’t keep an eye on your watch.
Tangent: Yes, I backpack with a wristwatch. I do almost everything with a wristwatch. Once on a trip along the Dirty Devil about a decade ago, Steve and I decided we wouldn’t bring a watch. After all, we were backpacking, we had all day, why be constrained by something so civilized as a watch? Why not wake when it gets light and go to sleep when it turns dark? Isn’t that the right, “natural” way to live?
It turned out to be a terrible idea. The trip was in October- a time of shortening days- and we spent most of the trip in deep-walled canyons under overcast skies. We never could never tell what time it was, and as we didn’t want to get stranded out day-hiking away from our base camp after nightfall, we really needed to know what time it was. As a result, we must have asked OCRick- who accompanied us on the trip but abstained form our little back-to-nature-wristwatch-rebellion- the time at least 30 times a day.
Continuing up around and above the alcove was the only tricky part of the hike, involving an exposed scramble up a series of ledges on the North side. Fortunately the rock of these ledges was distinctly different from that below or above- an extremely rough-surface, abrasive stone that was wonderful for free-climbing*. I’m pretty sure this was the Temple Butte Formation, a relatively narrow band between the Muav and the Redwall, that tends to be thicker in the West End of the Grand Canyon**.
The Temple Butte Formation is interesting in that it appears in channels in the underling Muav layer. The channels may have been streams or estuary channels within with deposits accumulated that became the Temple Butte rock some 350 – 400 million years ago.***
*But would be awful to fall or slide on.
**And which I either missed (entirely possible, as this geology stuff is still pretty new to me) or is absent in the main drainage of Tuckup Canyon.
***Different sources give really different ages for this layer.
After ascending 2 sets of ledges and crawling between 1 more (pic right), we were atop the alcove* and back in the Redwall, through which we continued up a drainage full of gullies, chutes, pockets, plazas and pour-offs. Every bend revealed some interesting little plaza or pool or minor obstacle (pic below, left)**.
*There’s a bolt at the top of the alcove. Rappelling down would be easier and safer than the ledgy down-climb
**This, BTW, is why hiking narrow canyons is so great to do with kids. The constant surprise-around-every-corner aspect and frequent scrambling opportunities distract them from the mundane-ness of trudging along for hours.
Eventually we broke out of the Redwall and the canyon, now just a shallow gully on the giant Esplanade terrace lined on either side by low shale hills. A short while later we crossed the Tuckup trail and arrived at the Cottonwood Spring. The Esplanade is dotted with a number of springs like this one. Here the hard capstone creating the terrace* serves at the hydrological barrier forcing the water to the surface.
*Which I described in Part 2 of this series.
The Spring was marked by a stand of young Cottonwoods (pic right). Standing snags suggested that much larger Cottonwoods used to shade the spot and we wondered why none of the giants still lived. At several point on our hike up we’d come across huge old trunks, even below the alcove, reminders of the force of floods that must scour the canyon.
The ground all around the spring was damp and grassy, and the grass here had a strange appearance, almost hazy, as though you couldn’t focus on it. On closer examination the “haze” was an abundance of super-fine stalks bearing seeds, like nothing I was familiar with.
Back home later I learned this was Western Panicgrass, Dicanthelium acuminatum (pic left, not mine), which is common across much of the US, but which I’d never before noticed in such concentrations. Panicgrass, BTW, belongs to the same grass sub-family, Panicodeae, as our old friend Crabgrass. While Crabgrass is an Old World native that has become a naturalized pest in the New World, Western Panicgrass is a New World native that has become naturalized pest in the Old.
Arriving at the spring we suddenly felt beat, and lazed for a while in the shade before heading down. After the Temple Butte down-climb we stopped in at the alcove again to pump some water, then picked our way down-canyon through lengthening shadows back to camp.
Next Up: The River.
Note About Sources: Geologic info for this post came primarily from Bob Ribokas’ Grand Canyon Explorer site, Stephen R. Whitney’s A Field Guide to the Grand Canyon and Wikipedia. Hanging Garden Info came from David Williams’ A Naturalist’s Guide to Canyon Country, and On The Distribution of Utah’s Hanging Gardens, Stanley L. Welsh, from the Great Basin Naturalist*. Welsh’s paper provided the algal species distribution info, but was apparently published before(?) the classification of Chrysophyta as Golden Algae, for which my primary source was the University of California Museum of Paleontology site. Panicgrass info came from the Master’s thesis, A Morphological Invesitagtion of Dicanthelium Section Lanuginosa (Poaceae), Justin Ray Thomas, Miami University.
*Now the Western North American Naturalist. Man, there is like a publication for everything.