Back in 1940, the United States Geological Survey (USGS)
issued Professional Paper 195 by W.P. Woodring, Ralph Stewart
and R.W. Richards, entitled: Geology of the Kettleman Hills
Oil Field, with the subtitle Stratigraphy, Paleontology,
and Structure. That's still pretty much the definitive geological
and paleontological statement on the Kettleman Hills region.
It's a classic work of science that continues to draw inquisitive
paleontology enthusiasts/sleuths to university reference libraries
all across America, seeking information on what kinds of fossils
can be collected there--and just where such magnificently preserved
material can be found.
For that data, you need to thumb all the way to the back
of the paper, through all of those stunning black and white photographs
of Kettleman Hills fossils--all of those perfectly preserved
sand dollars and pectens and clams and snails and such that truly
boggle the mind and catch one's attention, holding it for lengthy
periods of time, delaying the search for the exact localities
from which the specimens came. When you finally get to the back
of Professional Paper 195, one half expects to learn that most
of the fossils likely came from no more than a dozen or so localities,
20 to 30 at most, perhaps (I am speaking from experience--this
was my grand delusion, at least)--and so, it comes as a pleasant
shock to learn that the Kettleman Hills, an area roughly 20 miles
long by 4 miles wide situated some 80 miles northwest of Bakersfield
in Kings County, California, contain 370 registered fossil localities
in the Pliocene (5.3 to roughly 2.5 million years old) Tulare,
San Joaquin and Etchegoin Formations (in descending order of
geologic age--that is, from youngest to oldest)--an amazing array
of invertebrate, vertebrate and even floral fossil remains that
includes pectens (scallop shells), clams, gastropods, oysters,
mussels, fish, land mammals, marine mammals, sand dollars, diatoms
and even terrestrial plants, among others.
Of course, the majority of those 370 specific fossil localities
are no longer accessible to the general public; many remain closed
due to legal liability issues incurred by local property owners,
while others were obliterated long ago through the vagaries of
time. Most Kettleman Hills paleontolgical places of interest,
still potentially open for inspection, currently lie on private
property. That means, naturally enough, that if you've failed
to secure the essential preliminary formal written permission
from the proper authorities (the legal property owners), don't
even think about wandering off the main asphalt paths to seek
out potential fossil-bearing places. One will likely face certain
prosecution if one misbehaves here.
The three specific sites described here provide a representative
sampling of the kinds of fossils that can be found in the Kettleman
Hills area, as each is loaded with abundant, sensationally preserved
specimens. At last field check, only one of the localities requires
advance written documentation from the local oil corporation.
Probably the best of the lot, in terms of overall specimen
variety and quality of fossil preservation, is what many paleontology
enthusiasts refer to as--in an affectionate, colloquial sense--
"The Zone." The fish remains, pectens, oysters and
sand dollars found there occur in the Middle Pliocene San Joaquin
Formation, which is roughly three million years old, and the
Upper Pliocene Tulare Formation, around two and a half million
years ancient. It lies back in the Kettleman Hills on private
property, so permission must be secured from the oil company
branch office. Usually, though, that is not a problem. In any
event, the bottom line here is: You certainly must possess written
approval from the oil corporation folks before visiting "The
Zone" locality.
Averaging 10 to 20 feet in thickness, the fossiliferous
"Zone" horizon is a sequence of gray to tan silts and
sands exposed for a length of a half to three-quarters of a mile--it
is, in fact, an amazingly fossiliferous extension of the famous
Pecten Zone in the Middle Pliocene San Joaquin Formation. And
it is crammed almost everywhere one happens to look with perfectly
preserved scallops, oysters and sand dollars, primarily, whose
original shell material has been preserved intact.
In addition to the wonderful invertebrate animal assemblage
here, one is also advised to stay alert for occasional beaver
teeth--vertebrate remains that invariably, while on Public Lands,
one must leave alone, never collect except by formal written
permission from the Bureau of Land Management; but there, you
happen to fossil hunt on private property belonging to the oil
folks, and if you've successfully garnered the essential written
documentation from their branch office (let's hope that you have;
one needs to carry the paper at all times while on oil company
land, or risk almost certain detention by the local law enforcement
authorities while they decide whether to cite you for "simple"
misdemeanor trespass, or perhaps even criminal trespass), you
have secured the right to keep whatever fossils you happen to
find, including vertebrate remains usually off-limits to unauthorized
individuals.
At "The Zone" locality, the sand dollars measure
on average from a half-inch to two inches in diameter, although
many are quite minute--what you might call "sand pennies,"
if you will--in the neighborhood of no more than a quarter-inch
across. All such echinoid occurrences here are referable to one
or two species of the genus Dendraster, mainly Dendraster
coalingaensis. The scallop, or pecten shells are striking,
attractive specimens whose ribbed exteriors are of course very
distinctive and identifiable in the sediments; most of them belong
to the species Pecten coalingensis. An added collecting
plus here is that the majority of fossils either weather out
of the San Joaquin Formation already intact, or can be dug out
without any degree of pain or strain. All that's needed to put
the finishing, cleaning touches on them is a gentle scrubbing
in water with an old toothbrush.
In addition to the pectens, oysters, sand dollars and beaver
teeth teeth, another fossil type can be also found in the same
general area of "The Zone" locality--fish remains.
The specific horizon in which they occur has been mapped as the
Upper Pliocene Tulare Formation, which is about 2.5 million years
old. Geological and paleo-limnological analyses demonstrate pretty
convincingly that the Tulare is a fresh to brackish water deposit
that incorporates sedimentary facies which record the final drying
up of the last great inland sea to cover the present-day Central
Valley of California--a sea that throughout the Tertiary Period
of the Cenozoic Era (66 to roughly 2.5 million years ago) had
at times stretched from Redding (northern California) all the
way south to the vicinity of Bakersfield (southern California).
The Tulare Formation of the Kettleman Hills just happens
to yield the largest fauna of fresh water Pliocene mollusks of
any rock deposit on the US west coast. Some 33 varieties of pelecypods
and gastropods have been described from it, though only a few
species come from this particular spot near the The Zone. Several
miles south of The Zone locality, though, a second Tulare area
of exposure yields abundant and well preserved fresh water mollusks.
But here at "The Zone," fish remains are the
thing--unusual paleo-items colloquially called "bulbous
fish growths" by field geologists who've mapped the geology,
structure and stratigraphy of the Kettleman Hills. These are
the fossilized bony tumors which evidently afflicted many of
the fish during Tulare times. Most specimens are similar to observed
types that attack the skeletons of modern weak-fish, cod (specifically
the hakes), angel fishes and even catfish. No other fossil locality,
save the Kettleman Hills, is known to yield these kinds of paleontological
preservations. They are present in fair numbers in the tan silts
and sands, most appearing as rounded "bulbous" masses
that reveal obvious bony structure on their worn exteriors. A
few, though, show a definite resemblance in both shape and size
to Brazil nuts. This "bulbous fish growth" zone is
perhaps 30 feet thick at the most and trends generally south
to southeast for a distance of approximately three-quarters of
a mile. The fossilized bony tumors weather free from the easily
eroded sediments and presented no difficulty to collect.
While "bulbous fish" growths dominate the Tulare
exposures at "The Zone" site, much better preserved
pelecypods and gastropods from the Upper Pliocene Tulare Formation
occur several miles south in what local geologists call the Middle
Dome district of the Kettleman Hills ("The Zone" area
lies in what's referred to as the North Dome, by the way). Here,
innumerable freshwater gastropods and pelecypods weather out
whole and perfectly preserved. And because they're so exceedingly
fragile, special care must be taken to prevent them from incurring
damage. Probably a good idea is to place the mollusks in a plastic
sandwich bag for safe transport back home for a closer inspection.
Also present here, in the more indurated (hardened) layers of
sandstone, are relatively common specimens of brackish water
mussels, most of which occur in an excellent state of preservation.
Almost all of the 33 species of freshwater mollusks identified
from the Tulare Formation can be collected from this single locality.
An obvious distinctive feature of the assemblage is that in general
the fossil clams and snails are decidedly diminutive, many no
larger than a quarter-inch in length. For this reason, a good-quality
hand lens of ten power or better is useful when studying the
external details of your finds.
A third accessible and highly fossiliferous locality in
the Kettleman Hills occurs several miles south of the Tulare
locality; this one's within the Upper Mya Zone of the Middle
Pliocene San Joaquin Formation, a place that yields innumerable
three million year old pelecypods, many with both valves preserved
intact. It occurs in what's called the South Dome area of the
Kettleman Hills. Consisting almost entirely of estuarine clams
dominated by Mya dickersoni and Macoma affinis,
the pelecypodal fossils here are conspicuously abundant,
although several intervals reveal only fragmental material. Still,
many nice specimens of clams with both valves preserved can be
secured by using attentive care and extra patience. Even though
it's limited in aerial extent--the fossil-bearing layers outcrop
for only a tenth of a mile or so--this isolated exposure of San
Joaquin Formation sediments in the Upper Mya Zone provides a
maximum of clam-shell density, with Macoma and Mya
liberally distributed throughout the brown clays.
Now's probably a pretty good time to warn about a major
health risk while collecting fossils in the Kettleman Hills.
It's what's commonly called Valley Fever--a potentially
dangerous condition caused by inhalation of an infectious airborne
fungus. Not only are the Kettleman Hills affected, but the entire
surrounding southern San Joaquin Valley is also infested with
the fungal spores which cause Valley Fever, or what the medical
community calls Coccidioidomycosis. While most active cases of
the illness resemble a slight touch of the flu, or even a minor
cold, a small percentage of those infected do indeed go on to
develop severe medical complications such as pneumonia, meningitis
and even death; a particularly devastating, chronic form of "coccy"
mimics the debilitating symptoms of tuberculosis and lung cancer,
requiring months of recuperation and rehabilitation. On the other
hand, a significant percentage of those exposed to the fierce
fungus show absolutely no symptoms of any kind of infection.
In the southern Great Central Valley of California, there
is obviously no sure way to avoid exposure to coccy. For one,
it resides everywhere in the uncultivated alkaline soils of the
southern San Joaquin Valley (it's also endemic to California's
Mojave Desert, San Fernando Valley, Santa Clarita Valley, and
Coachella Valley--not to mention central to southern Arizona,
parts of New Mexico, southern Utah, west Texas, and southern
Nevada), and when the winds kick up, throwing dust everywhere,
one is almost certain to come in contact with the feared spores.
Fortunately, coccy is difficult for most folks to catch (individuals
with compromised immune systems seem most vulnerable), and only
a minuscule number of those who actually develop active symptoms
progress to the most severe complications.
This is all something to consider when stirring up dust
at the Kettleman Hills fossil localities, where in deference
to coccy's potential virulence many collectors choose to wear
surgical masks while excavating specimens.
If contending with Valley Fever fungal spores was not enough,
visitors to the Kettleman Hills experience even more obstacles
to paleontological nirvana. Although fossil collecting in the
Kettleman Hills can be done year-round, a couple of seasons in
California's Central Valley are notorious for, one, taxing bodily
comfort and, two, interfering with driving safety. Summertimes,
for example, are invariably ultrahot--downright savagely hot,
as a matter of fact--with daytime temperatures more like extreme
desert conditions than any other geographic comparison that comes
to mind. And there is no shade to speak of in the hills, except
for rare oven-tolerant shrubs maybe two feet high at most. These
are fine for shading the head when lying flat on one's back,
when prostrate, but rather puny for providing overall precautionary
protection from the elements. And while winters are usually mild,
with regular seasonal rainy patterns and tolerable temperatures,
a particularly impenetrable fog traditionally inhabits the Great
Central Valley during December and January--the infamous Tule
Fog. It clamps down tight on the entire San Joaquin Valley region
for days on end, at times reducing visibilities to zero. Needless
to report, driving during the reign of the Tule Fog is hazardous
and harrowing. And the Kettleman Hills, lying on the west side
of the Central Valley, do not seem to be exempt from these fogged
conditions. Proceed at your own risk then.
When collecting in the Kettleman Hills, be sure to obey
all the rules and regulations. Obtain written permission from
the oil company officials where necessary, and don't enter private
property without the owner's say-so. Of the three fossil localities
described here, only "The Zone" requires permission
from the oil corporation folks.
Happy collecting in the Kettleman Hills. But bring along
a hat and plenty of water in the summer. And a searchlight during
December--you never know when you might want to try to find the
end of your own nose in the Tule Fog.
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