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Field Trip To The Buffalo
Canyon Formation, Nevada
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 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, 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 spruce,
fir, pine, ash, maple, zelkova, willow and evergreen live oak.
Today, the fossilized remains of these
trees and shrubs, along with commercially mineable quantities
of diatomite can be found in the sedimentary layers deposited
in that ancient lake. In addition, several diatomite beds in
immediate vicinity of the plant-bearing place 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 K. L.
Barrows in 1971. The flora was most recently analyzed by the
late paleobotanist Daniel I. Axelrod in an excellent 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
America, and the Porcupine Mountains of Michigan. Based on the
environmental preferences of modern analogs of the fossil flora,
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 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. A good indication
of this can gained from comparing the average monthly temperatures
for the fossil site today with those estimated for the Middle
Miocene geologic times. For example, today's fossiliferous Buffalo
Canyon Formation terrain has an average June-July temperature
of some 77 degrees, but the fossil plants 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.
As far as estimating elevations of the
ancestral basin of deposition goes--Axelrod originally determined
that the plants preserved in the Middle Miocene Buffalo Canyon
Formation 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, recently, paleobotanists Howard
E. Schorn and the late Jack A. Wolfe (passed away in August,
2005) have demonstrated that the present-day Great Basin region
of Nevada stood just as high, if not higher, during Middle Miocene
times than it does today--accordingly, they propose that the
Buffalo Canyon Formation plants accumulated at an elevation of
roughly 9,000 feet, that in fact the entire Miocene Great Basin
area has dramatically dropped, collapsed, in elevations since
13 million years ago.
Altogether, some 54 species of fossils
plants have been secured from the famous paleobotanical district.
The two most conspicuous--and abundant--forms encountered 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.
According to paleobotanists Howard E.
Schorn (retired Curator of fossil plants at the University California
Museum of Paleontology) and Dr. Diane M. Erwin (present Curator
of fossil plants at UCMP), 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.
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, you're 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 the Middle Miocene Savage Canyon
Formation, 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 matter 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 show 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.
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 gully far below 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 natural 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.
It should be pointed out, perhaps, that
I recently donated practically all of my fossil plants from the
Buffalo Canyon Formation to the archival paleobotanical collections
at the University California Museum of Paleontology. 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 might have uncovered a
species that is new to science?
All of the collecting sites are presently
accessible: as far as I am aware, there are no collecting restrictions,
save the common-sense courtesy all the conscientious fossil hunters
abide by: always obtain permission from the owners before collecting
on private property. 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.
An excellent reference is a very informative
and well-written guidebook by Howard E. Schorn and Dr. Diane
M. Erwin, A Field Trip Guidebook To The Buffalo Canyon Fossil
Plant Locality, 10 May 1997, published by The Nevada Paleontological
Association in conjunction with the Carson City District Bureau
of Land Management. For some additional images of fossil plants
from the Buffalo Canyon district, check out a web page called,
Leaf Fossil Photos-Cenozoic.
A field trip to Buffalo Canyon, Nevada, will provide visitors
with something out of the ordinary: a chance to collect a large
selection of 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
west-central Nevada resembled the modern-day Klamath Mountains
of northwestern California and the humid, moist forests of the
Adirondack and Porcupine Mountains of the northeastern United
States.
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