Upheaval Dome, the most peculiar structural feature in southeast Utah

Severely contorted innards of Upheaval Dome.

Last September I visited two anomalous features on the generally orderly Colorado Plateau. The first was a cluster of igneous peaks in a sedimentary setting, to be the subject of a later post. I'm starting with the second—a large round hole in the ground. I thought it would be simpler.

The Colorado Plateau covers c. 130,000 sq mi in the Four Corners region in the southwest USA. For the last six million years it has been slowly rising, and yet it's remarkably stable, with limited deformation (NPS). Its wonderful landscapes are largely erosional, dominated by horizontal and vertical features. No wonder Upheaval Dome stands out.

Valley of the Gods shows the horizontal/vertical nature of the Colorado Plateau.

The remarkably round structure center left is Upheaval Dome (Google Earth; annotations added).

"Upheaval Dome" may seem an inappropriate name for a hole. However the rock layers surrounding it are indeed tilted, and though there's no top, geologists agree this is a dome. But what heaved it up is another matter. Wildly different theories have been debated for at least a century.

A decapitated dome with tilted strata encircling highly contorted rock; UGS photo, annotations added.

I would have loved to read the thoughts of the first geologists to peer over the rim! Surely they were surprised. But it appears this dome wasn't described until 1927, by which time it was already known to geologists—as Christmas Canyon Dome.

In the summer of 1926, petroleum geologist Thomas Harrison surveyed the area between the Colorado and Green Rivers, known to be underlain by a thick layer of salt. Elsewhere in the world buried salt created reservoirs for petroleum. Maybe this salt did too.

In his report Harrison explained that many of the domes he examined were gentle folds deserving further exploration. However there was a dramatic exception: "one discovered by Marland [Oil Co.] geologists shows a remarkable and very unusual development. This is the Christmas Canyon Dome." Harrison described a "sharp and highly distorted crest" and a "trough which closely and completely circumvents it" but that was all (1).

How could anyone look at Upheaval Dome and limit themselves to a one sentence description?! Perhaps Harrison didn't visit it himself, relying instead on discussions with Ben Parker of Marland Oil, who supplied a map and diagram.

Ben Parker's diagram of Christmas Canyon Dome; note steepness of deformed strata.

Harrison was not the only geologist working between the Green and Colorado Rivers in 1926. Edwin McKnight of the US Geological Survey was there too—mapping topography, describing and mapping rock units, investigating geologic structures, and assessing potential for manganese, oil and gas, among other things. After finishing in early summer of the next year, he promptly prepared a preliminary report. But the final report was delayed "by the assignment of the writer to other projects." Geology of Area between Green and Colorado Rivers was finally published in 1940, by which time Christmas Canyon Dome had become Upheaval Dome (2).

McKnight devoted five pages to Upheaval Dome, "the most peculiar structural feature in southeast Utah". He described it from the center outward. An interior conical dome, circular at the base, is surrounded by a ringlike syncline (narrow valley) and, beyond that, a circular ridge about a half mile wide. "The complete diameter of the affected area is 3 miles."

From map accompanying McKnight's report; Upheaval Dome is the tightly concentric red contour lines, 100 vertical feet apart (3).

The slopes of the interior dome were steep, generally 40–60º. But they ended prematurely, and the dome's summit was gone. Instead a large hole revealed spectacularly contorted innards. Here, McKnight couldn't hide his excitement:

"The White Rim member does not occur in place but appears as huge up-ended blocks the size of a house in the highly disturbed area of jagged pinnacles at the center of the dome. Surrounding this is the Moenkopi, very much crumpled and dissected by numerous gullies. The Shinarump [now part of the Chinle] forms a jagged fringe to the Moenkopi, its huge tilted triangular blocks sticking up like the teeth of a saw." [names refer to rock layers]

Huge tilted triangular block of the Shinarump sticking up like the tooth of a saw.

Just as amazing, though not so dramatic visually, are the rock layers immediately beyond the outer rim. They're horizontal! Intense deformation had been highly localized.

From McKnight's cross-section, labeled arrows added; note horizontal layers beyond the dome, and question marks inside it.

McKnight attributed the rise of Upheaval Dome to the thick layer of buried salt below, the one that drove Harrison's search for petroleum. It was deposited 300 million years ago in the great Paradox Sea, an inland sea sometimes connected to the ocean, sometimes not. When sea level dropped sufficiently, it was sucked dry by evaporation leaving thick salt deposits. Then the sea returned. There were on the order of 29 such cycles over a period of 15 million years, producing 6000 vertical feet of salt. With burial under younger sediments, it turned to rock.

Extent of the great Paradox Sea; courtesy Jack Share.

Salt is a sedimentary rock but an odd one—plastic and able to flow. It can move underground, accumulate and ooze upward, and deform overlying rock. Given the abundance of salt in the area, McKnight thought salt uplift the likely explanation for Upheaval Dome (4).

"Because of the known occurrence of thick salt under the Upheaval Dome, the writer prefers to consider this feature a salt dome. The rock in the center of the dome is greatly broken, mashed, and squeezed, as if it had been plastically kneaded ... The massive sandstones on the axis of the peripheral syncline also appear to have been deformed plastically and do not show the breaking and shattering that would be expected had they been deformed rapidly and near the surface. ... Every indication points to slow deformation under thick cover ..." (italics added).

Uplift is only part of the story behind today's Upheaval Dome. For millions of years after it rose, younger sediments were deposited over it, eventually becoming a cover of rock something like a mile thick (UGS). Then about six million years ago the Colorado Plateau began to rise. Streams were steepened and invigorated, enabling rapid erosion (NPS). Thousands of vertical feet of rock were removed, along with the summit of Upheaval Dome.

Upheaval Dome, revealed by erosion. Photo by Doc Searls.

The "salt theory" is fascinating, but it has problems. For example no remnants of salt have been found in the area of the dome (UGS). And seismic survey and drill holes have shown Paradox salt to be 1500 ft below the surface, i.e., well below the dome (Fillmore 2011). So the salt theory was modified. Perhaps Upheaval Dome is a salt diapir—created by a blob of salt that rose and was pinched off from its source below. Subsequent erosion removed it along with overlying rock, explaining the lack of salt remnants. But if this really is a salt diapir, it's the weirdest one ever, unlike any other in the world (Ornduff et al. 2006).

Fortunately there's another way to create a decapitated dome with highly contorted rocks and markedly localized deformation. And it can be done in less than a minute instead of 20 million years.

From NPS Upheaval Dome Trail Guide, 1993.

Perhaps c. 170 million years ago a meteorite slammed into this very spot. In the first tenth of a second, it would have greatly compressed the surface, and then sent a shock wave radiating outward, excavating a giant crater. This was followed by collapse of the crater rim and rebound of the compressed core, creating a dome of deformed rock. As in the salt theory, subsequent deposition buried the rebounded dome; then erosion removed the rock cover and top of the dome, exposing the contorted rocks inside. (Today's hole is NOT the impact crater, whose remnants were removed by erosion. But the two are easily confused.)

For years evidence had been accumulating in support of meteorite impact (e.g. Kriens et al. 1999). But there was a problem. No altered rocks singularly diagnostic of meteorite impact had been found. So the salt-meteorite debate raged on.

Then in 2008, Buchner and Kenkman proclaimed that impact origin for the "Sphinx of Geology" (Upheaval Dome) had been confirmed. They examined 120 thin sections of rock from the outer edge of the ring syncline and found shocked quartz, which only forms in meteorite impacts and nuclear explosions! Actually, the "vast majority" of the quartz grains in the rocks did not exhibit shock features. But they found two that did. These tiny "smoking guns" were said to be unequivocal evidence of meteorite impact.

The world of information adapted. Wikipedia declared meteorite impact the accepted theory. The Utah Geologic Survey announced that Utah's Belly Button, once considered an "outie" is now an "innie". My favorite southern Utah geo guides—Ornduff and pals—argued persuasively against salt, noting that "the most recent studies point to the meteorite theory".

As of 2024, the National Park Service wisely remains non-committal.

Yet there's still a problem. In addition to shocked quartz, Upheaval Dome has rock layers that clearly were tilted slowly, on the order of millions of years. So another possibility must be considered—perhaps a meteorite impact caused a salt diapir! (Daly & Kattenhorn 2010; Gessaman et al. 2015).

But I'm stopping here, having dwelt long enough on how Upheaval Dome might have formed. For me, the mystery doesn't diminish its chaotic and awesome beauty. In fact, it enhances it.

What hath God wrought?

Notes

(1) Harrison concluded that at Christmas Canyon Dome "beds have been too highly buckled and faulted" to justify exploration for oil.

(2) Thanks to the Utah Geologic Survey for supplying me with papers by early geologists, and for trying to solve the mystery of "Upheaval Dome" (the name). If you know its source, please Comment below.

(3) McKnight took pains to explain the unusual contour lines of Upheaval Dome: "The general shape of the dome and surrounding syncline is depicted with fair accuracy on plate 3, but because the information on which this part of the map is based was not detailed enough for mathematical representation of such features as the exact structural depth and configuration of the syncline and the exact closure on the central dome, the structure contours within the involved area have been dotted."

(4) As further evidence of salt deformation, McKnight noted that "Upheaval Dome closely approximates the theoretical form for salt domes under certain conditions", citing Nettleton, LL. 1934. Fluid mechanics of salt domes. Am. Assoc. Petr. Geol. Bull. 18: 175-1204.

Sources

The amount of information (and speculation) available for Upheaval Dome is truly overwhelming! These are sources I found useful.

Buchner, E. & Kenkmann, T. (2008) Upheaval Dome, Utah, USA: impact origin confirmed. Geology, 36, 227–230.

Daly, RG, and Kattenhorn, SA. 2010. Deformation styles At Upheaval Dome, Utah imply both meteorite impact and subsequent salt diapirism. 41st Lunar and Planetary Science Conference. PDF

Fillmore, R. 2011. Geological Evolution of the Colorado Plateau of Eastern Utah and Western Colorado. Includes lengthy discussion of competing theories.

Geesaman, PJ, et al. 2015. New evidence for long-term, salt-related deformation at Upheaval Dome, SE Utah. Abstract and slides.

Harrison, TS. 1927. Colorado–Utah Salt Domes. Am. Assoc. Petroleum Geologists 11:111–133.

Kriens, BJ, et al. 1997. Structure and kinematics of a complex impact crater, Upheaval Dome, southeast Utah. USGS.

McKnight, TS. 1940. Geology of area between Green and Colorado rivers, Grand and San Juan Counties, Utah. USGS Bull. 908.  [Upheaval Dome p 124–128]

National Park Service (NPS). Stretching of the Basin and Range and Lifting of the Colorado Plateau. Accessed Feb 2025.

Ornduff, RL, et al. 2006. Geology Underfoot in Southern Utah. Mountain Press. Vignette 28, "At the Mystery's Core", is about Upheaval Dome.

Share, Jack. 2011 (May 29). The Enigma of Upheaval Dome: Diapiric Salt or Ground Zero.

Utah Geologic Survey. Utah's Belly Button, once considered an "outie" is now an "innie". [UD is one of  many wonderful Utah GeoSites offered online, great for planning roadtrips.]

The Monthly Fern: Sensitive or Bead Fern

"... the fertile ones being so unlike the sterile, that no one who is unacquainted with the plant would suppose they had anything to do with each other." Photo by peganum.

As some readers know, I'm "working" on a Web-based guide to plants of South Dakota, a wonderful retirement project. Last year, once a month, I posted about a South Dakota tree starting with Black Hills Spruce, the state tree, and finishing with Osage Orange, God's Gift to the Prairie Farmer. It was such a pleasure and I learned so much! Inspired by the experience, I'm continuing in 2025 but switching to ferns (hence my fern holiday card).

First, let's be clear what ferns are (I needed this, Botany 101 being but a faint memory). Personally I think it's easier to describe what they're not. Ferns are neither mosses nor seed plants.

Ferns are like mosses in that they reproduce via spores. But unlike mosses, they have vascular tissue—pipe-like cells for transporting water and minerals through the plant. Because of this plumbing they're classified as vascular plants—tracheophytes. While mosses stay low to be near moisture, ferns can grow tall, even tree-size.

Brush Pot Tree (Sphaeropteris lepifera), a fern reaching for the sun. Photo by AraucariaHeterophylla.

Ferns are just a small subset of plants with vascular tissue. Tracheophytes include flowering plants, conifers, ginkos, cycads, and Gnetophytes (e.g. Ephedra, Mormon Tea). Unlike ferns, these plants reproduce by seeds, making them spermatophytes. 

Evolutionary diagram for plants; ferns and "Fern Allies" in green box. Geeks can click on image to view details (modified from source).

Ferns and the former Fern Allies used to be classified as pteridophytes, which you won't find in the diagram above. Turns out they're insufficiently related to qualify as a single taxonomic group. Even so, fern enthusiasts remain pteridologists, and infatuation with ferns is still referred to as pteridomania. I may well find myself in that state if the first Monthly Fern is any indication.

Sensitive Fern, Onoclea sensibilis. By rawpixel.

The Sensitive Fern is one of the oldest fern species still around. Its fossils go back at least 55 million years, and have been found in Greenland, western United States, Canada, Japan, United Kingdom and easternmost Russia (Moran 2004). Its distribution has shrunk a bit since; it grows in the eastern and midwestern US and eastern Asia. In South Dakota it does well in the Black Hills in the western part of the state, with a few scattered occurrences to the east. It seems to prefer moist to wet sites: stream and pond margins, wetlands, wet meadows and such.

Especially interesting are the leaves. There are two kinds and they differ dramatically, as pteridologist Daniel Cady Eaton explained (1881): "The fronds [leaves] are truly dimorphous, the fertile ones being so unlike the sterile, that no one who is unacquainted with the plant would suppose they had anything to do with each other." I agree!

The sterile leaves look like fern leaves—green and several times lobed. They're the basis for "Sensitive" as Eaton explained: "The fronds wilt very soon after plucking them ... The first frost of autumn destroys the sterile fronds; and a late frost in May or June does the same."

Sterile leaf of the Sensitive Fern. Photo by jillllybean.

In stark contrast, the fertile leaves are very odd! "The fertile fronds are not very common, and a young botanist may search in vain for them for a long time. ... They are nearly black in color ... [and] divided into a double row of sub-globose bead-like segments or pinnules; the whole looking like a small and narrow but dense cluster of diminutive grapes" (Eaton again).

No wonder Bead Fern is another common name. The beads are made of tightly rolled-up leaflet lobes, protecting spores waiting to fly in spring.

Sensitive/Bead Fern's curious fertile leaf (MWI).

Fertile leaves standing after sterile have wilted; var. interrupta, Japan. Photo by Aomorikuma.

Onoclea sensibilis from Eaton 1881. Emerton, JH, & Faxon, CE, illustrators.

The plate above shows two fertile bead-bearing leaves on the left, next to a large sterile leaf. But what's that leaf lower right? That was my question for Robbin Moran, eminent pteridologist and author of The Natural History of Ferns. He writes about the science of ferns with obvious and contagious joy, so I thought he might be willing to help.

Mystery leaf up close; arrows point to examples of possible sori ("spore clusters" for now).

A close look at the mystery leaf reveals what look like spore clusters, arranged as in many other fern species. "Is this a fertile leaf early in development?" I asked. No, but I wasn't totally off track, as Robbin explained:

"The leaf in the lower right is more highly cut (1-pinnate-pinnatifid), and such leaves are often produced late in the year, usually in response to trauma from mowing or a late frost. Sometimes these leaves represent a part-sterile and part-fertile condition, being developmentally intermediate between the two extremes of the normal sterile and fertile leaves ... " (2).

Intermediate leaves "often are produced in response to frost or mowing late in the season, although they also occur naturally without disturbance." (© Robbin Moran 2021)

Note elongate indusiate sori [spore clusters with little flap-like covers] (© Robbin Moran 2021). Oval lobes are maybe 5 mm long (my ball-park estimate).

With that mystery solved, we move on to spore dispersal. In Ferns of North America (also by Eaton, 1879–80) the Sensitive Fern plate includes an opened bead filled with what look like tinier beads. These are sporangia, which contain the even tinier spores (dust-sized!).

Open Sensitive Fern bead showing lobes and reproductive structures; when rolled up, beads are 2–6 mm long. From Plate LXXII in Eaton 1879–80.

Sensitive Fern in winter. Photo by Cephas.

By fall, Sensitive Fern's sterile leaves are gone and the fertile leaves look very much like dead plants. But they're not. Sometime in late winter the lobes of the beads begin to unroll in response to decreasing humidity. After enough drying, spores simply fall to the ground, perhaps to be blown away by wind (Suissa 2022).

That's so boring! Many ferns shoot their offspring out into the world, but not the Sensitive Fern. Sorry. The excitement of spore-shooting will have to wait for a future post.

Original source not given.

Notes

(1) Dimorphic sterile/fertile leaves are not unique to Onoclea sensibilis, but its leaves "differ drastically" (Beital et al. 1981).

(2) In the past, plants with intermediate sterile-fertile leaves have been recognized as a distinct species, a variety or a taxonomic form (e.g., Onoclea obtusilobata). Beital et al. (1981) showed none of these are valid. See also Flora North America.


Sources in addition to links in post

Beital, JM, Wagner, WH Jr., Walter,KS. 1981. Unusual frond development in Sensitive Fern, Onoclea sensibilis L. American Midland Naturalist 105:396-400. https://www.jstor.org/stable/2424762

Eaton, DC. 1879–80. The ferns of North America ... v. 2. Emerton, JH, & Faxon, CE, illustrators. Onoclea sensiblis Plate XII, pages 195–200. BHL

Eaton, DC. 1881. Beautiful ferns from original water-color drawings after nature. Emerton, JH, & Faxon, CE, illustrators. Onoclea sensiblis pages 153–158 & preceding plate. BHL

Moran, RC. 2004. The Natural History of Ferns. Timber Press.

Pinson, Jerald. About Ferns. American Fern Society (accessed 9 Feb 2025).

Suissa, JS. 2022. Fern fronds that move like pine cones: humidity-driven motion of fertile leaflets governs the timing of spore dispersal in a widespread fern species. Annals of Botany 129:519-528. https://doi.org/10.1093/aob/mcab137 (open access).