Sunday, November 16, 2014

Life of a Goblin

Rock goblins in the prime of life.
On Halloween I posted a day-appropriate geo-challenge.  The answer is ... Goblin Valley State Park in southeast Utah.  Here goblins live and die.  No one has measured their lifespan precisely, but we know it’s pretty short considering they’re made of rock.
Hundreds of goblins hang out near the parking lot, one of three large goblin gatherings in the Park.
Two young sandstone-capped goblins at sunrise, near the campground.  The cliff below them is a goblin nursery.
Younger goblins sport jaunty caps of sandstone that protect underlying softer rock for awhile.  But erosion takes its toll.  The goblins finally lose their caps and then vanish.
Two aging goblins on right.  The one on the left has vanished, leaving only its cap.
The geological term for goblins is "hoodoo".  There’s some disagreement as to what qualifies as a hoodoo.  There are broad definitions:
Hoodoos are tall [or not] skinny spires of rock that protrude from the bottom of arid basins and "broken" lands (National Park Service).
and more narrow:
a landform consisting of a column of clay or earth capped and protected from erosion by a boulder (Collins English Dictionary)
Capped hoodoos frequently are called mushroom rocks, and indeed Arthur Chaffin, who reported these hoodoos in the late 1920s, called the area Mushroom Valley.  Later it was acquired by the State of Utah and became a park in 1964, changing names along the way.

Undoubtedly Chaffin was not the first to see the goblins.  This is the land of the Ute people, and surely they had stories to explain the odd forms.  Indeed many look like animate beings turned to stone.  But it seems any such stories are lost.  In contrast, geologists have written down their story so we still have it.  It starts like this ...

Roughly 150-200 million years ago, a giant erg (dune field, like the Sahara) covered much of eastern Utah just south of a shallow sea.  Later the dunes were buried under terrestrial and marine deposits and eventually turned to rock.  Then the region was uplifted.  Erosion went to work, exposing the sandstone.  Weathering and erosion sculpted fantastic forms – arches, tafoni and hoodoos.  In 1928 two geologists, Gilluli and Reeside, formally named and described this particular sandstone – the Entrada (Milligan 2003).
The Entrada sandstone we all know and love – at Arches National Park in Utah.  Photo by Palacemusic.
Tafoni in Entrada sandstone at McInness Canyons National Recreation Area.
The Entrada varies from place to place because the original landscape varied; it wasn’t all dunes all the time.  Goblin Valley was a broad tidal flat about 170 million years ago (University of Utah no date), draining into the sea to the north.  This itself was a land of change.  There was the ebb and flow of tides, depositing sand and mud and then eroding it.  Tidal channels shifted.  Dunes came and went.  The shoreline moved as sea level changed.  There’s a record of all this in the rocks at Goblin Valley:  large-scale cross-bedding of ancient dunes, filled-in remnants of tidal channels, fine cross-bedding indicative of ebb and flood tides, and bands of different rock types – siltstone and shale as well as sandstone (Milligan 2003).  These interbedded strata are critical for hoodoo development.
Interbedded strata in the goblins also make up the wall behind, where erosion carves out new goblins.
Sandstone is harder and erodes more slowly.  It can protect underlying siltstones and shales to some degree.  But they still weather and erode, first becoming pedestals, then just piles after the sandstone cap falls, and finally part of the dirt around them.
Goblin in its "golden" years.  When the cap falls, the softer rock will soon disappear; note piles on right.
Goblin development depends on vertical cracks as well as horizontal layers.  It's in these cracks that weathering and erosion start.  Goblin Valley lies within an area where the Entrada is extensively faulted (Milligan 2003).  Just north of the Park are multiple sets of vertical microfractures that form blocks on a scale similar to goblin size.  It’s assumed that these occur in the Park too.
These goblins are still partly joined with their siblings.  Note vertical joints.
There may be a third factor in development – the degree to which sand grains are cemented together.  This might explain the oddly-shaped caps.  But no one has studied cementation in the Entrada sandstone in the Park.
The latest in goblin headwear.  Note cap-less piles in front -- dying goblins.
The cap in left mid-ground is called a turtle.
To visit the goblins, take Utah State Highway 24 southwest from Interstate 70 west of Green River, or northeast from Hanksville to the signed turnoff to Goblin Valley State Park.  Milligan (2003) described it as “one of Utah’s most remote and isolated state parks” but no such luck now.  It’s popular, especially in spring and fall.  The goblin overlook was busy on Friday and Saturday, but after a short hike into the desert I saw no one.  The small campground has nice but tightly-clustered sites (and a few yurts).  For $20 you can get a tent site and shaded table, drinking water, great scenery, and a free-but-challenging hot shower under a very narrow stream of water.

Panorama by Aaron D. Gifford; source.
Where on Google Earth (click on image for a better view).

Added Note:  I intended to explain that my camera had a tough time with color in goblin habitat.  I made some improvements with iPhoto, but many of the photos still look a bit surreal.


Sources

Milligan, MR.  2003.  Geology of Goblin Valley State Park, Utah, in Anderson, PB and Sprinkel, DA, eds., Geologic road, trail and lake guides to Utah's parks and monuments. UGA Publ 29.

Ornduff, RL, Wieder, RW and Futey, DG.  2006.  Geology underfoot in southern Utah.  Missoula, MT:  Mountain Press Publishing Co.

University of Utah.  No date.  Entrada Sandstone (in San Rafael Group).  Accessed November 2014.

Thursday, November 13, 2014

A visit to the First Ice Art of the Season exhibition


As you may have heard, the jet stream curved far north around a ridge of good weather and then curved south, followed by the infamous polar vortex ... or “winter” as we call it.  Indian Summer had been soooo beautiful, with highs in the 50s!  Then Winter came screaming in.
“I’M HERE!!!” announced Winter.
It was -22º F, but my new field assistant insisted we do our daily investigation of the river.
Winter's sudden arrival was a shock, and I can’t say I’m feeling all that great about it.  But there are antidotes.  One will be skiing once there’s enough snow.  Another is ice art.  Jack Frost followed close on the heels of Winter, and has been making his beautiful hoarfrost sculptures on the river ice.
Ice ferns, needles and stars (click on images to view).
The river was completely open three days ago.  Now it's mostly frozen over.  There are a few small openings with flowing water, but they won’t last.
A bit of open water.  Wood things in ice are anchored logs – fish habitat.
The frozen surface is covered with a mix of snow and hoarfrost.
What do beavers do in winter when the river freezes?  Hibernate in their lodge?  UPDATE:  Beavers don't hibernate; see note from Nina F in Comments.
Pile of sticks on left is a lodge.  Beavers were busy here earlier this year, what are they doing now?
The cottonwood tree on the left is the one I’m following.
I post about ice art every winter.  We are so lucky to have it ... thanks, Jack!
Jack Frost, from Central Park in Winter by Thomas Nast, 1864.

Sunday, November 9, 2014

Cottonwood Houses, Cottonwood Stars


Many years ago, in the heat of summer, little girls sat in the shade of cottonwood trees and made tipis from the leaves.
These they made in numbers and placed them in circles like the camp circle of their tribe.
“A circle of cottonwood-leaf toy tipis made by Indian children of Plains tribes” (Gilmore 1919).
I myself have spent a lot of time among cottonwoods as I’m following one this year – a lanceleaf cottonwood.  I’ve been keeping an eye out for stories.  I've found plenty, but none obviously about the lanceleaf.  It's definitely not the cottonwood of the toy tipi story.  The leaves are too narrow, and their bases are tapered.
Lanceleaf cottonwood, Populus x acuminata.
Most cottonwood stories probably refer to the Plains cottonwood, Populus deltoides ssp. monilifera.  It’s common in much of the American West, and was important to indigenous people, early travelers, and settlers – for shade, fuel and building materials.
A Plains cottonwood.  I ate lunch in its shade every day during a grassland project.
It was the Plains cottonwood – Wága chan of the Dakota – that supplied leaves for toy tipis.  In early October, I collected leaves from the Plains cottonwood in my yard, and spines from the matrimony vine (Lycium barbarum) to make my own, following the story carefully.
Building materials.
They split a leaf a short distance down from the tip along the midrib; at equal distances from the tip they tore across from the margin slightly; then, bending back the margin above the rents for the smoke flaps, and drawing together the leaf-margins below the rents and fastening them with a splinter or a thorn, they had a toy tipi.
Smoke flaps regulate draft and ventilate the tipi, especially smoke from the fire.
These [I] made in numbers and placed them in circles like the camp circle of [a] tribe.
The toy tipi story comes from ethnobotanist Melvin Gilmore (1919).  In the early 1900s he visited elderly Indians of the Great Plains who had gathered native plants and still knew the old names and uses.  He hoped to document this knowledge "while it may still be obtained, before the death of all the old people who alone possess it.”  They were happy to share the knowledge “in order that, as they said, future generations of their own people as well as the white people may know and understand their manner of life."

--- ✿ ✿ ✿ ✿ ✿ ✿ ✿ ---

Lanceleaf cottonwoods may not be good for leaf tipis, but like all cottonwoods, they do have stars inside.  The story of the cottonwood star comes from rural Nebraska, by way of Kathleen Cain (2007).  Her father once asked her “Have you ever seen the cottonwood star?”  She hadn’t.
He turned the twig so I could gaze directly into its center.  Running crosswise through the middle of the small piece of wood, the cut revealed a reddish-brown and nearly perfect five-pointed star.
You have to find one with a sturdy knuckle ... You have to cut cleanly ... No hacking.  Not jagged.  One cut is best.
A Pex tube cutter worked well.
A sturdy knuckle.
I selected a twig with a sturdy knuckle – the joint between two years’ growth – and cut through it easily and cleanly.  I saw a tiny reddish-brown spot, the pith where nutrients are stored and transported.  Then I looked through a 10x hand lens.  It was indeed a star!
A macro lens revealed the cottonwood star nicely.  It’s only 6 mm across.
The path of the hidden star stretches out into the future of every cottonwood branch.



Sources

Cain, K.  2007.  The cottonwood tree; an American champion.  Boulder, CO:  Johnson Books.

Gilmore, M.R.  1919.  Use of plants by the Indians of the Missouri River region.  Bureau of American Ethnology.

This post is part of this month's gathering of tree-followers kindly hosted by Lucy.

Wednesday, November 5, 2014

Cottonwood Encounters

Cottonwood leaf in mud.
Cottonwoods are common in the American West, even in the drier parts (they often mean water's close by).  I was pleased to meet three on my recent trip in eastern Utah.  The first was an old friend.  The second I've seen occasionally and always loved for it’s beauty.  The third was a complete surprise – new to me even though it’s quite old.

Cottonwoods lined the narrow road down Sheep Creek Canyon on the north side of the Uinta Mountains.  Some were golden, some were bare.  I assumed they were the narrowleaf cottonwood (Populus angustifolia), which is common in the Rocky Mountains, but when I looked close I found my old friend the lanceleaf cottonwood – same as the tree I’ve been following this year (Populus x acuminata).
Still fall in Sheep Creek Canyon ... but it's going fast.
Lanceleaf cottonwood grows at scattered locations in the Rockies.  It was described as a new species by Per Axel Rydberg in 1893, but has since been demoted to hybrid status – a cross between narrowleaf cottonwood and Plains cottonwood (P. deltoides).  Supposedly there’s no evidence that the lanceleaf reproduces by seed.  However it's been found hundreds of miles from its parents, suggesting that it’s self-fertile and “growing from its own seed” (more here).  Similarly, I saw neither narrowleaf nor Plains cottonwoods in Sheep Creek Canyon.  Perhaps Rydberg was right.
Lanceleaf cottonwoods with 300-million-year-old sandstone in Sheep Creek Canyon Geological Area.

I met the second cottonwood species on the south side of the Uinta Range, at the old homestead of Josie Bassett.  Josie staked a claim on the land in 1913 ... when she was 40, divorced, and with kids all gone.  She built a house, developed the cattle operation, and ran it alone until shortly before she died at 90.  The setting is spectacular.  The house sits at the mouth of a box canyon in steeply-tilted and intricately-carved Navajo sandstone.  Nearby I found the most beautiful cottonwood I’ve ever seen, in full autumn glory.  It was a Fremont cottonwood, glowing in the morning light.
Deciduous trees at the mouth of the box canyon mark the Bassett ranch.  Note golden cottonwood on right.
Populus fremontii, part of explorer John C Fremont's botanical legacy.
Fremont cottonwood has distinctive broad leaves with coarse rounded teeth.

My third cottonwood encounter was totally unexpected.  Actually I didn’t see the trees, but their leaves were unmistakable.  They lay perfectly preserved in 47-million-year-old mudstone of the Green River Formation (photo at top of post).
The great lakes of mid-Eocene time.  Lake Uinta was 270 across at maximum extent.
Apparently cottonwoods also were common 47 million years ago, back when the Uinta Mountains were bordered by large shallow lakes.  The climate was semi-tropical, perhaps like Florida's.  For 15 million years, fine sediments and debris containing plant and animal remains were deposited on the lake bottoms.  Now the sediments are rock – the Green River Formation – and the organisms are remarkably detailed fossils.
State Fossil of Wyoming – Knightia.  Source.
I was well aware of the abundant fish fossils of the Green River Formation.  They’re so common that one is the state fossil of WyomingBut I didn’t know about the plant fossils until I entered the Eocene Gallery at the Utah Field House of Natural History State Park Museum in Vernal.
A wall covered in plant fossils!
The leaf display was astonishing.  These leaves ended up on a lake bottom 47 million years ago, but they could just as well be last year’s, based on appearance.
This leaf fell off a tree 47 million years ago!
Fossilized sycamore leaf.
The scouring rush (Equisetum) below looks like our modern day ones.  Note the tiny teeth on the dark bands – the free tips of fused leaves – and possibly the remains of a cone at the top.  Below it is a modern-day scouring rush, also with a dark band of fused leaves, and a terminal strobilus (cone).
Photo by Bruce Leander via the Lady Bird Johnson Wildflower Center.
Slab of Green River mudstone with leaf fossils.
I was impressed by the the Field House.  How many communities the size of Vernal (9100 people) have a museum of this quality?  And why Vernal?  Because it sits in the heart of the Dinosaur Triangle, with a fossil record that is "embarrassingly rich" (not just dinosaurs). But it's mission is broader.  It includes interpreting the 80-mile radius around the town, including the Uinta Mountains.  I took in all the exhibits, covering geologic history from Precambrian to present.  They're modern, interesting, clear and justifiably enthusiastic ... if one takes time to read and look carefully.  A booklet explaining the exhibits in more detail is available at the front desk (worth the extra $2.50).
Stylinodon hangs out by a cottonwood tree on the shores of Lake Uinta.

Sources

Bennis-Bottomley, MB.  2012.  Fossil tales; an in-depth guide to the Utah Field House of Natural History exhibits.  Utah State Parks and Recreation.

Sprinkel, DA, Park, B and Stevens, M.  2000.  Geologic road guide to Sheep Creek Canyon Geological Area, northeastern Utah; in Anderson, PB and Sprinkel, DA, eds., Geologic road, trail and lake guides to Utah's parks and monuments.  UGA Publ 29.