Monday, July 9, 2018

Tree Report, Road Report


Not far from my house, halfway down a dirt road to the Laramie River, a boxelder grows in a nook formed by warehouse walls. This is the tree I'm following this year. I visit it early each month and report on what I find at the monthly virtual gathering of tree-followers, kindly hosted by The Squirrelbasket.

Since my visit in June, there's been a lot of plant growth in general. On disturbed soil and old railroad ties along the dirt road, pioneering plants were glowing in the morning sun. It’s impressive where they can grow and flourish! We should appreciate their ability to provide ecosystem services where nothing else can, but too often they’re considered “just weeds.”
Scotch or Cotton Thistle
Nuttall's Evening Primrose—some would say it's not weedy because the flowers are so pretty.
Foxtail Barley
It's a good year for Yellow Sweetclover! (there's a dog in there somewhere)
Several native prairie grasses have become established here too, probably from the small prairie near the river.
Needle and Thread
Indian Ricegrass
Next we crossed the dirt parking lot (empty, as it was a weekend) to visit the boxelder in its protected nook. It’s thriving, and looks so different from the spindly little tree of winter! I suspect rain runs off the roof, and that this spot is more hospitable than it appears.
Then ...
... and now.
These days the boxelder is all about leaves. Their tiny green factories (chloroplasts) are furiously gathering sunlight and cranking out energy for growth and storage.
Compound leaves, weird for a maple (genus Acer); more on this next month.

The boxelder’s neighbors are thriving too. Along the base of the warehouse wall, “weeds” have been growing fast, determined to reproduce before the season ends.
Yellow Sweetclover with Canada Thistle on either side.
Tumble Mustard (pale yellow flowers) surrounded by Canada Thistle. Cheatgrass front center.
Dock’s beautiful red wings are brown, but it’s still photosynthesizing, storing energy in its rhizomes.

After visiting the boxelder, I checked on the new road under construction. I’ve been following it too, after getting hooked by the amazing Gomaco 6300, which extruded curb-and-gutter like a pastry bag extrudes cake decorations. There's been a lot of progress, most recently signal lights, stripes and road signs. Best of all, in the evenings after the work crew has left, and on weekends, we can walk across the new bridge!
Then (Gomaco 6300 on left) ...
... and now.
New stop sign waits in a patch of Common Kochia, one of our tumbleweeds. Kochia is extremely common along the new road, and I anticipate lots of tumbleweeds in my yard next spring.
Nearing the crest of the new bridge.
Decorative street lights are a nice touch.
View south from the crest.
The horizontal green line is the terribly inadequate old bridge, to be torn down soon. Good riddance!
The road is scheduled to open by the end of July. Then the pleasure of a quiet stroll high above the railroad tracks will come to an end. But I’m not complaining. There's a sidewalk and a bike path too, and it will be a blessing to finally have a safe route across the tracks to the east side of town.


Join us … all are welcome!


Friday, June 22, 2018

Shelters in Tafoni (those curious holes in the rock)


Why do holes in a rock catch our eye? Is it because they’re unexpected? visually pleasing? photogenic? mysterious?
Tafoni all in a row, McInnis Canyons Recreation Area near Fruita, Colorado.
Resident unknown.

At Moonstone Beach (Cambria, California), tafoni are artistically arranged.

Tafoni wonderland at the Honeycombs in the West Desert of Utah.

Not surprisingly, geologists have a term for these curious holes—tafoni (singular tafone). But that doesn’t mean they know how they formed. The possibilities are many: salt weathering, variable rock composition, microclimates, pebbles falling out, and more. I’ve blogged on the topic here, here and here, and there’s an entire website devoted to tafoni. But this post isn’t about how tafoni form. It’s about how they’re used, specifically for shelter.
Tafoni at Montaña de Oro State Park, California, with makers’ remains still in place.
In some cases, how tafoni formed is revealed by the inhabitants—shellfish snug in cavities they themselves excavated. But more often, occupants move in long after the holes are created, for example packrats, which are especially fond of tafoni (these are native woodrats, not the invasive rats from Europe).

When a woodrat takes up residence, it begins to build a midden—a debris pile of fecal pellets richly augmented with plant fragments, bone, other animal dung, and anything else of interest (especially if it’s shiny!). The pile is cemented with urine, which hardens into protective crystalline amberat. Construction may continue for many generations, producing huge middens. In arid climates, packrat middens can last tens of thousands of years with the material remaining easily identifiable, making them important records of changes in vegetation and climate.

On a visit to the east end of the Uinta Mountains last month, I found a woodrat apartment complex! Or maybe these were single family dwellings with outbuildings—a residential style common in the rural American West. In any case, tafoni were clustered in sandstone on the escarpment side of a steep hogback. Small middens were common, made mostly of juniper bark and twigs, and occasional cactus fragments. The amount of amberat varied.
Above, tafoni occurred on the small hogback left of the superpositioned canyon on the right (Irish Canyon in northwest Colorado). Closeup below.
Many of these cavities have small middens.
Click on photo to view cactus areole with spines, near left wall of cavity.
Midden well-cemented with amberat.

A week later, at the Devil’s Kitchen in the Utah Black Rock Desert (not the better known burning-man BRD of Nevada), I came across tafoni in basalt in a lava flow—actually on a fault scarp in the flow. Long after the lava hardened, faulting created a wall 20 m high.
In one large cavity about 15 feet above the ground, something had built a nest out of sturdy interwoven sticks—definitely not a packrat.
I soon concluded the nest belonged to a raven or crow (probably raven, as crows use smaller materials). Just ten feet away, in a nook in the wall, I was surprised by three large young birds crouched on the ground. They stared at me with spooky blue eyes and opened their mouths, silently demanding food. They were downright creepy, and their nook reeked! I didn’t stay long.
This lovely bird-child is about a foot long. Is it a raven or a crow? (if you know, please comment)

After I left the Devil’s Kitchen, I drove many miles on gravel and dirt roads toward a pale mountain looming in the mist and light rain.
It was Crystal Peak, a tafoni wonderland! In keeping with the magical mood, the sun came out just as I arrived. But I had made a most regrettable error. One afternoon was far to little time to explore and experience a place as remarkable as Crystal Peak. On my next trip, I will spend several days there. And I will again go in spring, for Crystal Peak is a wonderland of plants as well as rocks.
My plan was to walk directly to the tafoni, but as soon as I got out of the pinyon-juniper woodland and onto gently rolling rock at the base of the wall, I was waylaid by plants. There were only a few under the pinyons and junipers, yet on the seemingly harsh rock I found a diversity of wildflowers, and wonderful bonsai-like trees and shrubs … amazing!

Pale leaves and reddish flowers belong to a wild buckwheat, Eriogonum sp.
One of our many paintbrushes, Castilleja sp.
Limber pine in a patch of mat spirea (Pinus flexilis, Petrophytum caespitosum).
The rock of Crystal Peak is volcanic—a rhyolitic ash-flow called the Tunnel Spring Tuff. Tafoni are abundant, and mostly elongated parallel to bedding planes (ash layers). They’re also surprisingly uniform in spacing, forcing geologists to scratch their heads (more on this later; Crystal Peak will have its own blog post in the near future).

The tafoni were extremely photogenic but challenging to photograph. The white tuff confused my camera. Occasionally it got it right and “saw” the rock the way I did:
… but more often it added brown tones:
Still, it was wonderful to look through the viewfinder—to observe scenes in detail and in new ways as I composed photographs. But my reverie ended when I realized I hadn’t seen my field assistant in awhile. Normally she’s always on the move, always investigating, always coming into view, never far away. I carefully scanned the white rock for a half-white dog. Finally I spotted her brown patches at the base of the wall. Among the tafoni, she had found one she liked—a perfect shelter.


This post is dedicated to geologist and Twitter friend @RonSchott (#GigaRon) who recently passed away, much too early! He always encouraged my geo-blogging and geo-tweeting, and I will miss him a lot.
Ron Schott early in his career (photo courtesy of his sister).