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).

Boxelder & Dock at Sunset

Boxelder (Acer negundo) in nook formed by warehouse walls.

The weekend came and went. Weekends are when I usually visit the boxelder I’m following—when no one is working at the warehouse where it grows. But last weekend was really windy, from dawn to dusk. So I waited for a calm evening, and after everyone had left for the day. Finally last night the wind died down at about 8 pm. After dressing for mosquitos, I walked over during the golden hour before sunset, when the sun’s rays pass through more atmosphere and the light is warmer, softer. The smoke plume from a forest fire southwest of town added to the effect.

Smoke plume from Badger Creek Fire.

The boxelder has changed dramatically since my last visit. A month ago, there were no leaves at all, and flower buds were opening on just one branchlet. Now all that’s left of the flowers are dead shriveled stamens (this is a male tree). Now it’s all about leaves—and leaflets, the boxelder’s leaves being compound.

Dangling remains of male flowers.

Boxelder's compound leaves are unusual for its genus—Acer (maples).

There were other changes. Along the base of the warehouse wall, sand dock, Rumex venosus, is in its full glory. Last month it sported flower buds. Now the achenes (seeds) have fully matured, and each is enclosed in inner tepals (undifferentiated petals) which have enlarged, developed reticulate veins, and turned bright pink … or rather a warm rose color in the golden light.

Reticulate veins visible to right of mid photo.

There are now Canada thistles (Cirsium arvense) mixed in with the dock.

Walking home, I saw a shaded patch of dock with the colors I'm used to:

This is my contribution to the June virtual gathering of tree followers, kindly hosted by The Squirrelbasket. Tree-following is fun! Consider joining us. More info here.

Botanical Perplexity in the Southern Utah Desert

The bush on the left isn’t dead.

On the Waterfall Trail behind the San Rafael Reef, west of Arches National Park, I came across an unfamiliar shrub. From a distance it looked dead, but up close I saw small green oval leaves with serrated upper margins, and fruit that looked like tiny immature apples. These suggested serviceberry, the genus Amelanchier, and I felt that pleasing cognitive dissonance that comes when something is both familiar and strange. I looked forward to solving the mystery, putting a name on this shrub.

The small glabrous (not hairy) leaves were problematic.

Developing fruit, with anthers and styles still visible.

Serrated leaves and pomes of Amelanchier (Juneberry, Serviceberry); source.

This was supposed to be a short post—put together quickly, just a few photos and some information about the serviceberry, finishing with a sunset. But identification proved elusive, in part due to the small glabrous (hairless) leaves that didn't fit any Utah species, but mainly because of the legacy of struggling Amelanchier taxonomists.

The overlapping and highly variable “species” of this genus confound even the experts. In 1946, eminent botanist Merritt Lyndon Fernald went so far as to claim that no other genus in North America, except perhaps Rubus and Crataegus (raspberries and hawthornes), offered as much “perplexity” as Amelanchier (1).

The serviceberry I saw along the Waterfall Trail is a case in point. For a century botanists have debated its status, moving it from species to subspecies to synonym and most recently back to species. Not surprisingly, my path through the literature was tortuous. But I did meet some interesting characters, starting with Ivar Frederick Tidestrom.

I.F. Tidestrom, photo courtesy USGS.

Ivar Tidestrom ran away from home in Sweden in 1880, and headed for the United States. He served in the US Army (cavalry), enrolled in the University of California as an engineering student, and soon switched to botany. In 1919 while collecting plants in the Charleston Mountains northwest of Las Vegas, Nevada, he found an unfamiliar serviceberry with small glabrous leaves in the “piñon belt near Wilson’s ranch”. Four years later, he published it as a new species: Amelanchier nitens.

Amelanchier nitens, collected by Ivar Tidestrom on May 27, 1919; US National Herbarium.

In the late 1930s, Ira Waddell Clokey, a mining engineer and botanist, was finishing up his intensive study of plants of the same Charleston Mountains. He went to Tidestrom’s site to collect more material of Amelanchier nitens. He concluded it didn’t warrant full species status. Instead, he called it Amelanchier utahensis ssp. covillei (Clokey 1945).

Ira Clokey died in 1950, just after his Flora of the Charleston Mountains was accepted for publication (source).

Around the same time, G. Neville Jones took on a revision of North American Amelanchier, published in 1946. He described Tidestrom’s serviceberry from the Charleston Mountains as an “extreme form” that “intergraded completely with the typical pubescent [hairy] forms” of Amelanchier utahensis, a widespread and highly variable species (2). Thus Amelanchier nitens was reduced to synonymy, becoming part of Utah Serviceberry, where it remained for almost 60 years.

The latest revision of Amelanchier was done by Christopher Campbell and five colleagues, for the Flora of North America (2015 online). In it, I found a species description that matched the serviceberries along the Waterfall Trail pretty well—Amelanchier nitens! So we’ve come full circle. Tidestrom’s serviceberry has been resurrected as a species, now with a common name—Shining Shadbush (shining for the glabrous leaves; shadbush is one of many common names for Amelanchier).

Does Shining Shadbush grow in the “piñon belt” of Utah?

Did I finally have a name for my mystery shrub? Maybe. Unfortunately, Shining Shadbush is said to grow only in the Charleston Mountains in Nevada and in a limited area near Sedona, Arizona, i.e., not in Utah. But then I read the fine print (emphasis added):

“The authors have observed incomplete herbarium specimens conforming to Amelanchier nitens morphology from Colorado, New Mexico, and Utah.”

So the serviceberries along the Waterfall Trail may be the Shining Shadbush, Amelanchier nitens. But given the “perplexities” of serviceberry classification, it’s probably best not to worry about a name. Instead, just enjoy Amelanchier’s approach to biodiversity!

Thus ends my winding tale ... except for the sunset. Here’s one looking south from the Waterfall Trail.

West side of San Rafael Reef, Henry Mountains in distance.

Notes

(1) In the Introduction to his American Species of Amelanchier, G. Neville Jones (1946) summarized the evolving struggle of taxonomists to classify serviceberries, with wild swings in numbers of species (emphasis added):

“The earlier students [19th century] of the North American flora, including Michaux, Pursh, Nuttall, Torrey, and Gray, took the view that [Amelanchier] in the western hemisphere consisted of only one, or at the most very few, highly variable species. … there now may be found in botanical literature nearly two hundred binomials and trinomials representing the species of Amelanchier in America.”

(2) Jones also described convincingly the challenge of serviceberry identification:

“Anyone who studies Amelanchier in the field, or who examines large series of specimens in herbaria, is at once struck by the extraordinary variation of the foliage that occurs even in the same species, as manifested in different stages of development and from various habitats. … When placed side by side, specimens of the same species in these different stages of development often show an almost incredible dissimilarity and have been not infrequently mistaken for different species.”

Sources

Most of these were accessed online via the Biodiversity Heritage Library. Their wonderful collection is newly enhanced with Full Text Search, more information here.

Campbell, CS, et al. 2015 (online). Amelanchier, Flora of North America vol 9. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=101333

Clokey, IW. 1945. Notes on the flora of the Charleston Mountains, Clark County, Nevada. Madroño 8:56-61. https://biodiversitylibrary.org/page/47877692

Clokey, IW. 1951. Flora of the Charleston Mountains, Clark County, Nevada. University of California Press (Amelanchier pp 119-120). https://books.google.com/books?id=GuBVI1nC-50C&source=gbs_navlinks_s

Jones, GN. 1946. American species of Amelanchier. Urbana: The University of Illinois Press (A. nitens pp 92-93). https://www.biodiversitylibrary.org/item/105913 

Tidestrom, IF. 1923. New or noteworthy species of plants from Utah and Nevada. Proceedings of the Biological Society of Washington 36:181-184. https://www.biodiversitylibrary.org/page/34510710#page/201/mode/1up

Tidestrom, IF. 1925. Flora of Utah and Nevada. Contributions from the United States National Museum 25 (Amelanchier nitens pp 282-284). https://catalog.hathitrust.org/Record/001494238