Field Trip To The Kettleman Hills Fossil District, California

Please Note: Unauthorized fossil collecting anywhere in the Kettleman Hills is strictly verboten, prohibited. Visitors must first secure in writing formal permission from the property owners.

Lots of paleontology enthusiasts have heard of the Kettleman Hills, have in fact observed at any number of rock and fossil shows the magnificent Pliocene sand dollars and Pectens, in particular, that can be collected there.

Here's an opportunity to take a cybervist visit to three specific fossil-bearing localities in the Kettleman Hills that yielded many species of wonderfully preserved invertebrate fossil specimens.

And now for the obligatory words of caution. Endemic to the Kettleman Hills and the southern San Joaquin Valley of California, in general, is Valley Fever. This is a potentially serious illness called, scientifically, Coccidioidomycosis, or "coccy" for short; it's caused by the inhalation of an infectious airborne fungus whose spores lie dormant in the uncultivated, harsh alkaline soils. When an unsuspecting and susceptible individual breaths the spores into his or her lungs, the fungus springs to life, as it prefers the moist, dark recesses of the human lungs (cats, dogs, rodents and even snakes, among other vertebrates, are also susceptible to "coccy") to multiply and be happy. Most cases of active Valley Fever resemble a minor touch of the flu, though the majority of those exposed show absolutely no symptoms of any kind of illness; it is important to note, of course, that in rather rare instances Valley Fever can progress to a severe and serious infection, causing high fever, chills, unending fatigue, rapid weight loss, inflammation of the joints, meningitis, pneumonia and even death. Every fossil prospector who chooses to visit the Kettleman Hills and southern San Joaquin Valley must be fully aware of the risks involved.

Take The Field Trip

For More Images Of Fossils From The Kettleman Hills Click Here

For Images Of Fossils From The Vicinity Of The Kettleman Hills Click Here

Back in 1940, the United States Geological Survey 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, a classic work of science that continues to draw many 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 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, distinct fossil localities in the Pliocene (4 to roughly 2 million years old) Tulare, San Joaquin and Etchegoin Formations (in descending order of geologic age--that is, from youngest to oldest)--a huge array of invertebrate, vertebrate and even floral fossil remains that includes Pectens (scallop shells), clams, gastropods, oysters, mussels, fish remains, land mammals, marine mammals, sand dollars, diatoms and even terrestrial plants, among others.

Of course, many of those 370 specific fossil localities are no longer accessible (due to Oil Company policies/restrictions,), but there still remain a tantalizing few productive places where amateurs and professional paleontologists alike continue to collect loads of exquisitely preserved fossils from that remarkable series of Pliocene geologic rock deposits that record the ancient animal and plant life of the last great inland sea to cover the present-day Central Valley of California, a sea that at one time or another, during the Tertiary Period of the Cenozoic Era (65 to about 2 million years ago), stretched from Redding all the way south to the vicinity of Bakersfield. Unfortunately for amateur paleontology sleuths, they're all privately owned sites, where one must secure explicit written and verbal permission from the land owners before even dreaming of collecting there. The three specific sites described here used to provide a representative sampling of the kinds of fossils to be found in the area, and each of them was loaded with abundant, well-preserved specimens.

Probably the best of the lot, in terms of overall variety of fossils, is what many paleontology enthusiasts referred to as "The Zone," in an affectionate, colloquial sense. 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 to 1.8 million years ancient. It lies back in the Kettleman Hills on Chevron Oil Companies property, so permission, before the entire area was closed off to private collectors, had to be secured from the Chevron Companies branch office in Bakersfield, California, some 80 miles southeast of the Kettleman Hills, before any visit was made. Usually, though, that was not a problem. But, the bottom line here is: You certainly had to possess written approval from the Chevron folks, requesting formal permission to collect at "The Zone" locality.

Click on the picture below for a larger image depicting the Kettleman Hills fossil field; the view is roughly northeast across the Kettleman Hills from "The Zone" fossil locality.

Averaging 10 to 20 feet in thickness, the fossiliferous 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. Here, one was advised to keep one's eyes open for the occasional beaver teeth, too, 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 happened to collect on private property belonging to the Chevron Companies, and if you had successfully garnered the essential written documentation from their branch office in Bakersfield (let's hope that you had; one needed to carry the documentation at all times while on the oil company's land, or risk almost certain detention by the local law enforcement authorities while they decided whether to cite you for "simple" misdemeanor trespass, or perhaps even criminal trespass), you had secured the right to keep whatever fossils you happened to find, including vertebrate remains usually off-limits to unauthorized amateurs. The sand dollars measured, on average, from a half-inch to two inches in diameter, although many were quite minute--what you might call "sand pennies"--in the neighborhood of no more than a quarter-inch across. Yet, even such seemingly unpreservable, fragile remains had been faithfully kept whole for some three million years. All of the sand dollars are referable to one or two species of the genus Dendraster, primarily Dendraster coalingaensis. The scallop, or Pecten shells are striking, attractive specimens whose ribbed exteriors were very distinctive and identifiable in the sediments; most of them belong to the species Pecten coalingensis. An added collecting plus here was the fact that the majority of the fossils either weathered out of the San Joaquin Formation already intact, or could be dug out without any degree of pain or strain. All that was needed to put the finishing, cleaning touches on them was a gentle scrubbing in water with an old toothbrush.

Click on the picture below for a larger image. Here is a representative sampling of the fossil goodies that could be collected from "The Zone" locality: all the sand dollars are Dendraster coalingaensis; the scallop, or Pecten shells belong to Pecten coalingensis. 

In addition to the Pectens, oyster, sand dollars and beaver teeth teeth, another fossil type could be found in the same general area of "The Zone" locality--fish remains. The specific horizon in which they occur lies within the Upper Pliocene Tulare Formation, which is about two million years old; geologists consider the Tulare to be a fresh to brackish water deposit that represents the final drying up of the great inland sea which, during Pliocene times, five to 1.8 million years ago, stretched from present-day Red Bluff south to the vicinity of Bakersfield. The Tulare Formation of the Kettleman Hills yields the largest fauna of fresh water Pliocene mollusks of any rock deposit on the West Coast. Some 33 species of pelecypods and gastropods have been described from it, although only a few have came from this particular spot near the The Zone site. A second site in the Tulare, though, several miles south of The Zone locality, yielded abundant well preserved fresh water mollusks.

But here at "The Zone" site, fish remains were the thing--unusual fossils colloquially called "bulbous fish growths" by field geologists who've mapped the geology of the Kettleman Hills. These are the fossilized bony tumors which evidently afflicted many of the fish during Tulare times. Most of the fossil tumors 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 specimens. 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. Simply scooping them up when found, wrapping the specimens in tissue paper or paper towels and then storing them in a plastic bag usually protected all the fossil bony tumors quite nicely.

Click on the picture below for a larger image. Here, a paleontology enthusiast explores the famous Pecten Zone in the Middle Pliocene San Joaquin Formation, "The Zone" locality in the Kettleman Hills, long before the area became inaccessible due to oil company liability issues. It was very difficult to traverse this slope without stepping on the whole, perfect sand dollars that had weathered out of the fine silts and sands, some three million years old.

Much better preserved clams and snails from the Upper Pliocene Tulare Formation occurred several miles south of "The Zone" site 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 tiny freshwater gastropods and pelecypods weathered out whole, perfectly preserved. Because they were so exceedingly fragile, special care had to be taken to prevent them from getting damaged. It was best to place the mollusks in a plastic sandwich bag until you transported them home for a closer inspection. Also present here, in the more indurated (hardened) layers of sandstone, were relatively common specimens of brackish water mussels, most of which were in an excellent state of preservation. Almost all of the 33 species of freshwater mollusks identified from the Tulare Formation could be collected from this single locality. A distinctive feature of the assemblage was that, in general, the fossil clams and snails were very small, many no larger than a quarter-inch in length. For this reason, a good-quality hand lens of ten power or better was useful when studying the external details of your finds.

By the way, this is a pretty good place to mention that when exploring for fossils in the Kettleman Hills, if you had fail to secure formal written permission from the proper authorities (the legal property owners), one shouldn't even think of searching for potential fossil-bearing places. One will likely face certain prosecution if one misbehaves here.

A third accessible, highly fossiliferous locality in the Kettleman Hills occurred several miles south of the Tulare locality; this one was within the Upper Mya Zone of the Middle Pliocene San Joaquin Formation, a place that yielded innumerable three million year old pelecypods, many with both valves preserved intact; it occurred in what's called the South Dome area of the Kettleman Hills. Consisting almost entirely of brackish water pelecypods belonging to Mya dickersoni and Macoma affinis, the fossils here were conspicuously abundant, although several zones reveal only fragmental material. Still, many nice specimens of clams with both valves preserved could be collected by using some extra care and patience. Although limited in aerial extent--the fossil-bearing layers ran for only about a tenth of a mile--this isolated exposure of San Joaquin Formation sediments in the Upper Mya Zone provided a maximum of clam-shell density, with Macoma and Mya liberally distributed throughout the brown clays.

Click on the picture below for a larger image; here is a representative sampling of pelecypods that could be collected from the San Joaquin Formation "clam quarry" in the Kettleman Hills--a site that lies within the Upper Mya Zone. All specimens are Mya dickersoni, except for the following, which belong to Macoma affinis: second and third specimens from left, top row; third specimen from left, middle row; and third specimen from left, bottom row.

Although fossil collecting in the Kettleman Hills could 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 was no shade to speak of in the hills, except for rare oven-tolerant shrubs maybe at most two feet high. These were 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 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 valley, do not seem to be exempt from these fogged conditions. Proceed at your own risk then.

When visiting the Kettleman Hills, be sure to obey all the rules. Without first securing formal written permission from the Ketlleman Hills property owners, no fossil collecting is permitted.

Fossils From The Kettleman Hills

Please Note: All fossil specimens figured here were collected long before the Kettleman Hills became off-limits.

A pecten (scallop) shell from the Middle Pliocene San Joaquin Formation, Kettleman Hills, California. Called scientifically Pecten coalingensis. 

 This is a sand dollar from the Middle Pliocene San Joaquin Formation, Kettleman Hills, California. Called scientifically, Dendraster coalingensis.

 A gastropod from the Middle Pliocene San Joaquin Formation, Kettleman Hills, California. Called scientifically, Neverita reclusiana.

 Oysters from the Middle Miocene San Joaquin Formation, Kettleman Hills, California. Called scientically, Ostrea vespertina sequens.

A "bulbous fish growth" from the Middle Pliocene San Joaquin Formation, Kettleman Hills, California. This is a fossilized boney tumor that afflicted a fish that lived some 4 million years ago in the estuaries bordering a great inland sea in what is now the Central Valley of California. Most of the fossil tumors 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 specimens. 

 Fossil fresh water gastropods from the Upper Pliocene Tulare Formation, Kettleman Hills, California. Called scientifically, Physa wattsi.

Fossils Collected From The Vicinity Of The Kettleman Hills, California

Water Beetle 

 Sand Dollars

 Giant Oyster

Turritellas; Barnacles

 Turritella Snails

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