|Visit an extraordinarily productive 15-million-year-old fossil locality in, Nevada, a number of miles from Fallon--a place that has yielded some 54 species of ancient plants from the middle Miocene Buffalo Canyon Formation.|
The Buffalo Canyon Formation lies in the heart of the arid Great Basin physiographic province a number of miles from Fallon, Nevada, home to the US Navy's Top Gun fighter pilot program. This is a land characterized by three widely distributed botanic species: sagebrush, juniper, and pinion pine. But roughly 15.5 million years ago, during middle Miocene geologic times, the present-day fossil locality was the site of a large fresh-water lake around which flourished a great variety of plants, including but of course not limited to--spruce, fir, pine, ash, maple, zelkova, willow, and evergreen live oak.
Today, common to abundant carbonized leaf and seed impressions from over 50 species of trees and shrubs, along with commercially mineable quantities of diatomite (a microscopic photosynthesizing single-celled plant), can be found in the sedimentary layers deposited in that ancient lake. Not only that, but several diatomite beds in the immediate vicinity of the plant-bearing locality have been changed to prized opal through the geologic forces of heat and pressure, a geologic process that has created abundant, colorful material for hobby, recreational lapidary use.
All of the fossil plants occur in the diatomite member of the middle Miocene Buffalo Canyon Formation, a regional badlands-forming deposit originally named by geologist K. L. Barrows in 1971.
Credit for discovering the fossil plant-bearing beds at Buffalo Canyon goes to a Mrs. Beulah Buckner, who came across the productive diatomaceous beds during a rockhounding excursion in either the 1940s or very early 1950s. After she eventually directed writer Harold O. Weight and his wife Lucile to the locality, Mr. Weight wrote up an article on the subject of fossil plants in Buffalo Canyon for a noted national publication, in which he named one of the primary fossil-bearing sites Fossil Leaf Hill.
Interestingly enough, many years later, completely unaware of Mr. Weight's earlier published documentation of the Buffalo Canyon fossils, I happened to re-discover that same leaf and seed-bearing locality and decided to call it Fossil Leaf Ridge. The thought of course occurred to me at the time that probably loads of folks have independently "discovered" that identical prolific plant-yielding site over the decades.
The most efficient way to locate fossil plants here is to split the soft shales along their natural bedding planes. Use the pick end of a geology rock hammer or a broad putty knife to split the poorly indurated, often crumbly sedimentary material. If you should happen to accidentally fracture a fossil specimen, use Duco Cement or some other fast-drying, reliable glue to mend the break. But try to be especially careful not to crack the fossils. Attempting to glue pieces of diatomaceous shale back together is usually a messy, delicate chore. Several coats of glue applied along the fractured surfaces may be required to get the job done, since the porous, powdery rocks often soak up glue like the proverbial sponge.
Not every sedimentary rock layer in the area is fossiliferous--as a matter of fact there appear to be many more barren horizons than plant-bearing ones. But, generally speaking, if you can find the fine-grained, whitish diatomaceous shales that outcrop in proximity to narrow beds of blue-gray volcanic ash, your chances of finding superior fossil plant specimens will increased dramatically. The "paper shales" observed in parts of the section closely resemble the plant and insect-bearing shales exposed in Fossil Valley, Nevada, and Florissant, Colorado--noted insect-yielding deposits of world-wide renown--although I've yet to locate anything significant in the Buffalo Canyon sediments, save for a few poorly preserved leaf fragments. Still, those paper shales may well be worth some special explorations. Excellent specimens could yet show up in them, due to the fact that they lie in such close stratigraphic proximity to the plant-bearing beds higher in the geologic section. Adding to the paper shales' potential interest is the fact that, recently, a graduate student on a field trip to Buffalo Canyon uncovered an exquisitely preserved dragonfly wing--the very first fossil insect reported from the middle Miocene Buffalo Canyon Formation.
The shales in the Buffalo Canyon Formation grade upward into geologically younger tan to gray clays and sandstones bearing five distinct beds of lignite, a brownish-black coal whose alteration of the original vegetal constituents has proceeded farther than in peat but no so far as in subbituminous coal. All five layers of the lignite have been analyzed for possible uranium content, but only two of the beds showed any potential economic interest, averaging 0.052 to 0.1 percent uranium. The ashy-gray mudstones in this part of the geologic section frequently yield abundant remains of reeds from a species of cattail, a scouring rush.
Taken together as evidence, the lignites and fossil cattails indicate ponded, swampy conditions during deposition of the younger phases of the middle Miocene Buffalo Canyon Formation. The regularly bedded diatomaceous shales lower in the section--rocks which represent the older periods of deposition--were likely laid down in a large lake whose shoreline supported a dense growth of deciduous hardwood trees and shrubs such as maple, birch, ash, cottonwood, willow, serviceberry, hawthorn, Oregon grape, bitter cherry, currant, rose, and sparkleberry. Slightly higher slopes bordering the basin of deposition were covered by a rich mixed conifer forest of fir, larch, spruce, cypress, hemlock, maple, alder, birch, black locust, elm, zelkova, serviceberry, hawthorn, Oregon grape, bitter cherry, and mountain ash. On the more exposed, drier south and west-facing hillsides the mesic vegetation graded into an evergreen woodland consisting of madrone, mountain mahogany, cypress, stopper, juniper, catalina ironwood, and evergreen live oak.
The Buffalo Canyon fossil flora was most recently analyzed by the late paleobotanist Daniel I. Axelrod in an informative monograph. Axelrod concluded that the fossil floral association most closely resembles conifer-deciduous forests now living in three widely separated areas of the United States: the Klamath Mountains of northwestern California; the Adirondack Mountains of eastern Americal; and the Porcupine Mountains of Michigan.
Based on the environmental preferences of modern analogs of the fossil flora, Axelrod decided that precipitation in the ancestral Buffalo Canyon Basin was approximately 35 to 40 inches per year, a figure that contrasts radically with the scant 15 inches delivered there today--and most of that amount is in the form of winter snow. A major difference in the rainfall patterns 15.5 million years ago was that storms dropped significant amounts of precipitation during both the winter and summer months--enough rain during those seasons, as a matter of fact, to account for such sensitive indicators as elm, birch, hickory, black locust, and zelkova in the local fossil record.
Temperatures were also apparently much more moderate some 15.5 million years ago. For example, terrain in proximity to today's fossiliferous Buffalo Canyon Formation experiences an average June-July temperature of some 77 degrees, but the associations of fossil plants now found there prove that 15 million years ago the average monthly reading for that specific time of season could not have been any higher than 63 degrees. And while today's average January temperatures range downward to a frigid, arctic-style 10 degrees, the mid-Miocene plants demonstrate that 15.5 million years ago a typical January mean would have been a rather chilly, but tolerable 37 degrees.
Such a major change in Buffalo Canyon's precipitation and temperature averages over geologic time suggests that elevations there differed significantly some 16 to 15 million years ago. Cogitating this perplexing problem, Axelrod studied in great detail the environmental requirements for today's analogs of species found in the Buffalo Canyon Formation to determine that the plants likely accumulated at an elevation of roughly 4,200 feet; today, the fossil site lies at an altitude of 6,060 feet, suggesting, according to Axelrod's analysis, that the region has undergone an uplift of approximately 1,900 feet since middle Miocene times 15.5 million years ago.
But, that was not the end of the "uplift" story. Far from it. Eventually, the late paleobotanists Howard E. Schorn and Jack A. Wolfe, along with several other scientists working the problem independently, applied sophisticated geophysical, geochemical, and Climate Leaf Analysis Multivariate Program methodology (CLAMP) to conclude that the present-day Great Basin region of eastern California (Death Valley region), Nevada, southeastern Oregon, southern Idaho, and extreme western Utah stood just as high, if not higher, during middle Miocene times than it does today. Accordingly, when all the evidence from disparate avenues of analysis finally came together, Schorn and Wolfe proposed that the Buffalo Canyon Formation plants accumulated at an elevation of roughly 9,000 feet, that in actual fact the entire Cenozoic Era Great Basin region--the so-called Nevadaplano--had remained a vast high plateau region for most of the early to mid Teriary Period (Paleocene, Eocene, Oligocene, and lower to middle Miocene Epochs), until at last that Nevadaplano gradually dropped, collapsed, to its modern-day elevations by 13 million years ago through geologic extensional stress and concomitant block faulting which helped create the modern Great Basin geography.
Today, roughly 15 million years after Buffalo Canyon Lake ceased to exist, dried up--a moment in geologic time before the Nevadaplano high plateau completely collapsed--some 54 species of fossil plants remain in the rocks to tell their fascinating paleobotanical tales. The two most conspicuous, and abundant, forms encountered in the Buffalo Canyon Formation are intact leaves from an evergreen live oak, Quercus pollardiana--a species that is practically identical to the living maul oak now native to the western foothills of the Sierra Nevada, Cascade Mountains and Coast Ranges of California--and leaves from a birch, Betula thor, whose vegetation is identical to the the modern paper birch. Other less commonly observed specimens include the leafy twigs of cypress, a juniper, in addition to the leaves of cattail, four species of cottonwood, six species of willow, an alder, three additional species of birch, a hornbeam, a hickory, a black walnut, two more species of oak, an elm, a zelkova, two species of holly grape, a water lily, a hydrangea, four species of currant, a Catalina ironwood, three species of bitter cherry, a rose, a mountain ash, a leadplant, a black locust, a tropical cypress, a madrone, a stopper, two species of ash, a sparkleberry, and a snowberry. Also present, but rarely recovered, are the winged flying seeds of two species of fir, one species of larch, three species of spruce, two species of pine, one species of Douglas-fir, one species of hemlock, and five species of maple.
During my last extended exploration of the Buffalo Canyon Formation, I spent a couple of productive days opening a modest-sized fossil quarry. The digging was good. Among my keepers were several nice birch leaves, winged spruce seeds, a few relatively rare Zelkova leaves, and many nice evergreen live oak leaves. A few years later I made a brief stopover to check out my quarry, which had lain dormant all that time. Unfortunately, I found it had been obliterated by heavy rains. All that was left to mark the site of my past digs were several large slabs of shale I remember having yanked out while attempting to expose a particularly fossiliferous layer upon which were plastered some fine specimens of oak leaves. The slabs of shale had been washed way down slope into a newly formed natural gully far removed where I had dug--the result of intense, short-lived rampaging runoff that had taken advantage of the softer sedimentary rocks there, cutting into them with potent ease: acts of inexorable erosive power on full display here. I spent a couple of hours digging in the same general area as my original quarry and was pleased to learn that the fossil plants were still "alive and well;" they could still be found there, much to my delight.
All of the collecting sites are presently accessible: as far as I am aware, no federal or private ownership collecting restrictions exist. Still and all, conscientious fossil aficionados will nevertheless opt to conduct common sense due diligence to determine the current legal accessibility of the fossil locality before visiting. And, of course, should commercial collecting parties begin to raid and desecrate the fossil plant localities, the Bureau of Land Management will most certainly close the fossil leaf-bearing district to all but professional paleontologists.
It should be pointed out, perhaps, that eventually, after several years of conducting occasional visits to the much-productive district, I decided to donate practically all the fossil plants I'd recovered from the middle Miocene Buffalo Canyon Formation to a major museum's archival paleobotanical fossil repository. As a general rule, all particularly well-preserved plant remains collected from the area should be brought the attention of a professional paleobotanist; who knows, perhaps you have uncovered a species that is new to science!
A field trip to Buffalo Canyon, Nevada, will provide visitors with something out of the ordinary: a chance to collect a large selection of nicely preserved middle Miocene plant remains, plus an abundance of very colorful specimens of common opal, as well. As you dig into the fossiliferous diatomaceous shales of the middle Miocene Buffalo Canyon Formation, you will bring fossil leaves and winged seeds to their first light of day in some 15 million years, species which tell of a time when the plant life in this part of arid Nevada resembled the modern-day rain-rich Klamath Mountains of northwestern California and the humid, moist forests of the Adirondack and Porcupine Mountains of the northeastern United States.
|Click on the image for a larger picture. The view is southeast to the southern end of a plant-bearing outcrop of the Middle Miocene Buffalo Canyon Formation--the whitish slope at upper left quadrant of the image.|
|Click on the image for a larger picture. Looking essentially due east to the west-facing slope of one of the primary fossil plant-bearing sites in the plant-bearing district. Relatively common, excellently preserved fossil leaf and winged seed impressions occur from about one-half to three-quarters the way up the moderate slope. Note the relatively flat-lying diatomaceous shales and mudstones of the Middle Miocene Buffalo Canyon Formation, which yields some 54 species of plants.|
|Click on the image for a larger picture. The view is roughly south along the west-facing slope of a fossil plant-bearing section. The 15-million-year-old leaf and winged seed impressions occur in the diatomite member--composed almost entirely of the microscopic single-celled aquatic plant called diatoms) of the Middle Miocene Buffalo Canyon Formation: leaves of evergreen live oak and the paper birch are the most commonly encountered remains.|
|Click on the image for a larger picture. A complete leaf from the evergreen live oak, Quercus pollardiana, which is similar to the living maul oak, now native to the western foothills of the Sierra Nevada, Cascade Mountains and Coast Ranges of California; this species is a co-dominant of the flora.|
|Click on the image for a larger picture. A mostly complete leaf (stem is missing) from the evergreen live oak Quercus pollardiana, a Miocene analog of the living maul oak, native to the Sierra Nevada and other mountain ranges of California.|
|Click on the image for a larger picture. Here is a complete specimen of a zelkova leaf, a member of the elm family, Zelkova brownii. Out of some 8,276 fossil plant specimens that paleobotanist Daniel I. Axelrod collected from the Buffalo Canyon Formation, he found only 744 zelkova leaves.|
|Click on the image for a larger picture. A winged seed from a spruce, Picea sp. Not sure which species it came from---it appears to most closely resemble a variety Axelrod called Picea lahotense, a spruce whose closest modern analogs are now native to eastern Asia.|
|Click on the image for a larger picture. A common cattail leaf from the Middle Miocene Buffalo Canyon Formation, Churchill County, Nevada, Typha lesquereuxi.|
|Click on the image for a larger picture. Here is a mostly complete leaf (the tip is missing) from an alder, Alnus latahensis, which is the fossil equivalent of the modern Seaside alder now native to Maryland and Delaware in the United States of America.|
|Click on the image for a larger image. A twig from a species of juniper called Juniperus desotoyana, which is closely allied with the living Eastern Red Cedar, or the Pencil Cedar, native to North America, from Hudson Bay, all the way south to Florida. and Texas. Of course, it is not a true cedar at all--it is a variety of juniper.|
|A Water lily seed pod called scientifically Nymphaeites nevadensis. Image courtesy of Howard Schorn, retired Collections Manager of fossil plants at the University California Museum of Paleontology.|
|Click on the image for a larger picture. Specimens of high grade, commercially minable diatomite from the Middle Miocene Buffalo Canyon Formation, Buffalo Canyon. Diatomite is composed almost entirely of microscopic single-celled aquatic plants called diatoms.|
|Click on the image for a larger picture. Pieces of common opal from contact-altered beds of diatomite in Buffalo Canyon; specimens are likely too fractured for serious lapidary use, but there's a lot of the colorful material available for recreational rockhounding purposes.|