Tuesday, October 10, 2017

Goodbye Sabalites ... Hello Boxelder?

If I had an extra $85,000 (64,000 £), I could have Sabalites right here in my own home! Then I wouldn’t need to travel (5-foot slab, Denver rock show; photo courtesy Mike N).

* * *

For the second time, bad weather foiled my plan to travel to southwest Wyoming to visit what was once the home of Sabalites—a fossil palm I was following. Just like in mid June, a surprise spell of rain, snow and cold arrived. But this time I knew it would get colder, not warmer, so I'm moving on—choosing another tree to follow for the year to come.

After four years of tree-following, I now have realistic criteria for choosing a tree. Actually, there are only two: easily accessible and dynamic. It needs to be somewhere that I can get to on short notice if necessary, and in whatever weather. And it needs to do things! or be where things happen. There are some impressive conifers not far away, but from our perspective, they hardly change through the year. So I’m considering deciduous trees in or very close to town.
The cottonwood on the Laramie River that I followed in 2014 (photo taken yesterday).
A leading candidate is a boxelder (aka ashleaf maple, 3-leaf maple, Acer negundo) just five minutes from my house. It’s a tough little “street-tree” that manages to survive in the light-industrial / riparian ecotone on the edge of town (ecotone = biological transition zone). This area is vegetated mostly with herbaceous species—Canada thistles, dandelions, tumbleweeds, knotweeds, and such. Most people call them weeds, but really they’re pioneering species able to colonize disturbed sites (like yards). I think they’re under appreciated, which is another reason I’m interested in following this tree.
Being deciduous, the boxelder will reveal a lot more about its life than a conifer would—buds, flowers, leaves, changes in color, and surely things I can't predict. The next photos show it at the height of the growing season in 2015. [Recently, the old palettes and trash that accumulated in this nook were hauled off. Hopefully no one will decide to remove the boxelder in the interest of urban renewal!]

Now, most of the leaves are dead, killed by frost. Interestingly, the few that catch late afternoon sunlight still show signs of life.

Living where it does, human activity will contribute drama to the boxelder's life—delivery trucks, trash that comes and goes, and, for the next year, road construction.
Boxelder in corner by parked car.
Road construction in foreground, Murdoch's warehouse in mid-ground, riparian habitat in distance. 
The big cranes on the skyline are installing a new bridge across the railroad tracks.


Monthly gatherings of tree-followers are kindly hosted by The Squirrelbasket. Consider joining us; it’s easy and always interesting! More information here.


Thursday, October 5, 2017

Castle Gardens Art & the Missing Turtle

What’s the message here?

In my post last week about the impressive junipers at Castle Gardens (near Riverton, Wyoming), I only briefly mentioned the petroglyphs. That was because they deserve a post of their own. They’re fairly famous, in part for their style, which is unusual enough to have a name: Castle Gardens Shield Style. And the site is a poster child for rock art vandalism, most notably because of the missing Great Turtle.

Castle Gardens used to be part of the Love Ranch, where legendary Wyoming geologist J. David Love was born and raised (see John McPhee’s Rising from the Plains). In 1931, while an undergrad at the University of Wyoming, he told eminent archeologist EB Renaud about the petroglyphs, and served as guide during surveys.
All black-and-white photos are from Sowers (1941).
Renaud was impressed with the number and distinctiveness of the petroglyphs. Many incorporate circular “shields” with various designs and objects enclosed in the circles. In some cases, paint was added. We don’t know how often images were painted; only small faded patches and hints of color remain. However, the process of preparing the “canvas” is still discernable. The sandstone face was smoothed, and the weathered outer layer removed, likely with some kind of stone tool. Then the artist created an image by incising narrow lines, perhaps with bone, stone, or antler … or maybe metal if the petroglyphs are as young as some experts think (source).

According to Renaud (1936), the most impressive petroglyph was the Great Turtle:
“It is 16.5314 inches (42 cm) across and also with short outside rays, and in good state of preservation. The figure is very neatly engraved and carefully colored in three shades, the same as the other drawings, green, orange-yellow and purplish-red. … There are 60 such sections, 46 on the elliptical carapace, 13 for the legs and one for the triangular head. The ensemble forms a very attractive polychrome mosaic …”
But by 1940, when photographer TC Sowers traveled to Castle Gardens, the polychrome turtle was gone—chipped out! Supposedly word of the atrocity spread through the region, with threats attached. In any case, a year later the Great Turtle was “anonymously donated” to the Wyoming State Museum in Cheyenne, where it’s part of the Native American permanent exhibit.
“This is a copy of an original photograph taken by Mr. Love …”
Above, the Great Turtle now resides in a controlled climate at the Wyoming State Museum, along with an “artistic interpretation” of the petroglyph at the time of creation, below.

Vandalism continued at Castle Gardens, in part because the site was so remote that vandals could work at their leisure. There have been several attempts at protection. Access to the site was improved in the hopes that more visitation would increase appreciation, and minimize opportunities for destruction. But vandalism continued, and the rise in visitation produced a network of user trails and bare areas. So graveled paths and chainlink fences were added. The fences are an intrusion, no question, but there seems to be no alternative.
Graveled walkway leading into the heart of Castle Gardens; revegetation project in foreground.
Above, panel photographed in 1941; below, in 2017 (through a chain link fence).
Online, webpage after webpage notes that Castle Gardens are well worth a visit, in spite of the damage and fences. I agree. The petroglyphs are clear to the eye and intriguing to the mind … who made them? and most importantly, why? What were they saying?! After my visit, I searched and read, assuming I would find out. Instead I learned that there are few answersvery few that are generally accepted. But I should have known. How could we possibly read the minds of people long gone?
“We know very little …” (Wyoming State Museum).

Rock art is notoriously difficult to date in the absence of paint or a well-developed patina on the rock (for carbon dating), so it’s difficult to say who made it, or whose ancestors. The artists may have come and gone long ago, their artwork being their only lasting legacy. But archeologists keep trying. Renaud (1936) concluded that Castle Gardens petroglyphs were quite old, “in fact prehistoric.” He found no indication of horses or other items that arrived with Europeans. And the Arapaho and Shoshoni Indians living nearby “deny any knowledge concerning meaning and makers …” Others have concluded that the makers were Shoshonean, with ties to modern day Shoshoni culture (e.g., Francis & Loendorf 2002; quoted here).

But many experts object to interpretation based on culture of modern-day (and presumed) relatives. That distant world and the inhabitants it shaped had to have been very different from today. Through what mental constructs did they view reality? What were their needs? Did they hope to discourage invaders, impress cooperators, flatter those in control of the weather and the hunt? Were they temporarily escaping the harshness of daily life? We do that too—we try to shape reality through art, stories, imagination, fantasy. Surely we have that in common with these ghostly beings whom we know only through petroglyphs.
“The past is a foreign country: they do things differently there” (LP Hartley, The Go-Between; Kelly 2016).
Are there vultures in the center shield?

In her article about prehistoric art (The New Yorker, June 23, 2008), Judith Thurman noted that there are two kinds of experts: “those who can’t resist advancing a theory about the art, and those who believe that there isn’t, and never will be, enough evidence to support one.” I’m sure I would be in the latter camp if I were an archeologist. But I’m not. So I'm free to enjoy the possibilities.

One of the more appealing explanations of the Castle Gardens petroglyphs is that they represent trance visions or shamanism. Perhaps these artists were among the select few able to leave the harsh reality of life and cross into other worlds. They recorded their “travels” using images on rock. Maybe hundreds of years later, Shoshoneans discovered them and took them to be magical. Tales grew around them, and were passed down and elaborated to become today’s legends. Maybe we do the same. In the petroglyph below, I immediately saw a celestial alignment—like the total eclipse of the day before!


Sources (in addition to links in post)

Francis, JE, and Loendorf, L. 2002. Ancient visions: petroglyphs and pictographs of the Wind River and Bighorn country, Wyoming and Montana. Salt Lake City: University of Utah Press.

Kelly, RL. 2016. The fifth beginning: what six million years of human history can tell us. University of California Press.

Randall, AG. 1964. Pictographs and petroglyphs of the Castle Gardens area, Fremont County, Wyoming. The Wyoming Archeologist 7:21-25 (PDF).

Renaud, EB. 1936. Pictographs and petroglyphs of the high western plains, in Archeological survey of the high western plains, 8th Rept. Included in Randall 1964.

Sowers, TC. 1941. Petroglyphs of Castle Gardens. Report by the Wyoming Archeological Survey, sponsored by the University of Wyoming, Works Progress Administration. Included in Randall 1964.

Thurman, J. 2008. First impressions; what does the world’s oldest art say about us? The New Yorker (June 23).


Friday, September 29, 2017

Common Junipers at Castle Gardens

Not what you think when you read “castle gardens”?

After my total eclipse experience, I stayed to explore the empty country of central Wyoming, first visiting Castle Gardens at the suggestion of a friend. She had warned me: “There’s no castle and no gardens!” But in fact I found castles galore, with interesting elegant gardens, though a bit sparse. It was a pleasure to stroll, clamber, and slide back down through them.
“… the jagged edges of an eroded anticline are projected sharply above the surrounding plain … the wind has carved many of these vividly colored sandstone rocks into fantastic shapes and the landscape is dotted here and there with green pines, cedars and berry bushes, the effect is of some medieval castles surrounded by quaint gardens—hence the name Castle Gardens.” Dave Love (1)
After driving many miles on gravel roads through dry rolling “empty” country, I headed east on a rough dirt road through the “eroded anticline” that Dave Love described 85 years ago. Tilted rock layers formed multiple low ridges. The steep pale sandstone faces were fairly soft, but they were capped with resistant rock that has protected them from obliteration by erosion. But only for awhile. Eventually the protective caps will be undercut and fall away, and erosion will proceed apace.

I could see large roughly-circular patches of green scattered across the barren slopes. That’s one hardy plant, I thought, growing so vigorously where nothing else can. But what is it? I was intrigued. I hiked up a slope to check, and found a familiar shrub—common juniper! What a surprise to see it in such dry, harsh, unforgiving habitat.
Note big green patches on distant slopes.
Common juniper is indeed common here.
Erosion is an issue, along with the usual heat and drought of the high desert.
But this was only a surprise because of my perspective. I’ve seen lots of common juniper—for example in ponderosa pine forests in the Black Hills, limber and in lodgepole forests in the Laramie Mountains, and on subalpine and even alpine sites in the Medicine Bow Mountains. But I now know that common juniper must have arrived on those sites before the trees, perhaps after fire or logging or some other disturbance. For its seedlings are intolerant of shade and competition.

Common juniper generally requires open habitat to become established. It “reaches maximum abundance on harsh, stressed environments in which competition is lacking” (source). The Castle Gardens area certainly qualifies. I suspect these junipers are doing well in part because they tap into water that accumulates in fractured rocks below the surface, produced by the tilting mentioned above. I've seen this elsewhere (e.g., here).
Thriving even!

True to its name(s), common juniper (Juniperus communis) is common; in fact it's said to have “the largest geographic range of any woody plant” (source), growing throughout the northern hemisphere in cool temperate areas. In the American West we know it as a shrub, but in the northeastern USA it occasionally reaches tree size, and trees are common in Europe. This isn't just a change in size, but also architecture, with one or a few stems becoming dominant.
Juniperus communis in the Netherlands (source).
Juniper “berries” are actually cones—like tiny pine cones but with fleshy scales (you can geek out on definitions here). Berries of the common juniper are used to flavor gin. They take several years to mature, becoming blue-purple.
Source.

Back at the car: "Hot day, let’s drive somewhere and enjoy the AC!"

While many of the steep sandstone slopes were nicely sculpted, none really qualified as a castle. To see castles I continued east on the dirt road to the Castle Gardens Petroglyph Site, managed by the Bureau of Land Management (2). Amazingly there are two Castle Gardens in Wyoming. The other is near Tensleep.

The gardens among the castles were dominated by limber pine (Pinus flexilis), juniper (probably Juniperus osteosperma), and of course common juniper.
Did the limber pine get started in the protection of the common juniper?

Contrary to its name, there is an uncommonness to common juniper. It's the only juniper in North America with needles; the others have scales. But if you’re familiar with any of the scale-leaved junipers, you’ve probably seen needles on the seedlings and young growth. It's thought that common juniper has needles because it never makes the transition to mature scales. In other words, common juniper never grows up.

But I wonder if that’s really the case. The needles of common juniper (and the two other species in sect. Juniperus subsect. Juniperus) differ from the immature needles of scale-leaved junipers in that there’s a joint where they attach to the stem. In scale-leaved junipers, needles transition smoothly (photo below). Is this significant? I don't know; my online searching was fruitless. But that’s okay—I’m happy that Nature provides such interesting things to ponder.😀
Left, common juniper needles; right, immature needles of Juniperus chinensis (source).


Notes

(1) Castle Gardens used to be part of the Love Ranch, where legendary Wyoming geologist J. David Love was born and raised (featured in John McPhee’s Rising from the Plains). In 1931, while an undergraduate at the University of Wyoming, he described the site to archeologists, served as guide during survey, and provided information for their report (Renaud 1936).

(2) Vandalism of Castle Garden petroglyphs has been horrendous. It’s sad to compare today’s situation with early descriptions and photos. But the site is still worth a visit; the artwork is wonderful, and trails and fences have been built recently to protect the petroglyphs. A post about them will appear here next week.


Sources (in addition to links in post)

Randall, AG. 1964. Pictographs and petroglyphs of the Castle Gardens area, Fremont County, Wyoming. The Wyoming Archeologist 7:21-25 (PDF).



Monday, September 18, 2017

Wyoming's Exotic and Enigmatic Phonolite

Folks, it’s phonolite!

In the late 1970s, I worked as a ranger naturalist at Devils Tower National Monument in northeast Wyoming. During my stints at the desk in the Visitor Center, I heard the Admatic Automatic Slide Projector’s short program about the Tower over and over. One phrase is especially memorable: “phonolite porphyry, named for the ringing sound the rock makes makes when struck.”

I thought it would be fun to demonstrate this for visitors, but I was never able to produce a ringing sound by striking the Tower rock. Interestingly, the Park Service now says that “phonolite (fō'nə-līt') refers to the mineral composition of the rock.” However “porphyry” hasn't changed; it still refers to rock texture—visible crystals (in this case feldspar) in a fine-grained matrix.
Northeast face of Devils Tower.
Futilely striking Tower rock.
Devils Tower phonolite porphyry.
Phonolite is an uncommon rock—“exotic and enigmatic.” Yet I encountered it again just recently, in the Rattlesnake Hills of central Wyoming only 175 miles southwest of Devils Tower. In both places the phonolite is estimated to be about 40 million years old, emplaced during the Eocene Epoch.
Phonolite is igneous—formed from magma. It’s often referred to as volcanic (e.g., here and here), which means it's extrusive—magma reached the surface. And yet the Devils Tower and Rattlesnake Hills phonolite bodies are considered intrusions that formed below the surface, though probably not deep. The phonolite in the Rattlesnake Hills has been called “subvolcanic.”

Devils Tower is just one of a collection of igneous intrusions of Eocene age in the northern Black Hills. Rock types include members of the phonolite-trachyte-latite series. They probably were emplaced late in the uplift of the Hills (part of the Laramide Orogeny, the building of the Rocky Mountains). The intrusions were later exposed by erosion, and now form prominent landscape features: Devils Tower, the Little Missouri Buttes, Sundance Mountain, Inyan Kara Mountain, Crow Peak, and more.
Sundance Mountain; note columnar jointing (click on image to view).
During cooling and contraction of the intruded magma, columnar jointing sometimes formed. As Evelyn Mervine has said, “Columnar jointing is always a joy to observe in rocks in the field. Stumbling upon perfectly geometric columns of rock can only be described as magical.”

Many northern Black Hills intrusions include columnar jointing, but never as extensively and dramatically as at Devils Tower—not even close! There the columns are as much as six feet across and 600 feet tall.
South face of Devils Tower.

Like the Black Hills, the Rattlesnake Hills were created during the Laramide Orogeny. They also include Eocene igneous intrusions. Composition is similar to those of the Black Hills, but phonolite is more common, found in 21 intrusions in the central core of the range (Hoch and Frost 1993). Columnar jointing occurs here too.
Igneous intrusions ahead! Dry Creek Road along the southwest flank of the Rattlesnake Hills.
Goat Mountain is latite.
Round Mountain is phonolite.
Columnar jointing on Round Mountain.
Columnar jointing east of Dry Creek Road; rock type unknown (phonolite-trachyte-latite series).

The same rare rocks of about the same age in close proximity demands an explanation! Are Black Hills and Rattlesnake Hills intrusions related? Sadly, it appears no one knows. Their origins are “poorly understood” and the phonolite remains enigmatic. Hoch and Frost (1993) think that Laramide structural features (faults, fractures) “enabled the alkaline and subalkaline magmas to ascend to shallow crustal levels.” But why would there be exotic magmas here?

Geochemical analyses indicated that the magmas must have involved some mixing. But Archean country rocks of the Wyoming craton—our several-billion-year-old basement rocks—are poorly represented in the mix. Hoch and Frost wrote that the magma “may reflect the composition of subcontinental mantle that has been isolated and chemically modified during the last 3.5 billion years.”

In other words, magma made from deep 3.5-billion-year-old rocks moved up through fractures 40 million years ago, and solidified before reaching the surface. Then starting around five million years ago, erosion carried away the overlying softer rocks, revealing the intrusions. If correct, this will be a really cool story! But more work needs to be done. The phonolites are not eager to give up their secrets.
North face of Devils Tower. “It is somewhat of a geological puzzle, standing alone as it does, and rising directly out of a country entirely made up of sedimentary rock.” Thomas Moran, 1894


Sources

Hausel, WD. 1996. Geology and gold mineralization of the Rattlesnake Hills, Granite Mountains, Wyoming. Wyoming Geological Survey Report of Investigations No. 52. http://www.wsgs.wyo.gov/products/wsgs-1996-ri-52.pdf Accessed 17 September 2017.

Hoch, AR, and Frost, CD. 1993. Petrographic and geochemical characteristics of mid-Tertiary igneous rocks in the Rattlesnake Hills, central Wyoming, with a comparison to the Bear Lodge intrusive suite of northeastern Wyoming, in Snoke, AW, Steidtmann, JR, and Roberts, SM, eds. Geology of Wyoming. Wyoming State Geological Survey Memoir 5:508-528.

Sutherland, WM, and Hausel, WD. 2002. Preliminary geologic map of the Rattlesnake Hills 1:100,000 quadrangle [Wyoming]. Wyoming State Geological Survey OFR 2002-2. http://www.wsgs.wyo.gov/products/wsgs-2002-ofr-02.pdf Accessed 17 September 2017.

For more on the puzzling geology of Devils Tower, see The many views of Devils Tower.