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Roger Weller, geology instructor

La Brea Tar Pits
by Beckett Chmura
Physical Geology
Spring 2007

The La Brea Tar Pits


            The La Brea Tar Pits are, as the name suggests, pits of tar (more formally known as asphalt). Throughout the history of time, numerous creatures have fought a sticky tar battle and, on numerous separate occasions, lost. These hundreds of pits are formed over thousands of years through an accumulation of seeping asphalt and, interestingly, are located in Los Angeles, California. There is no other place in the world quite like The La Brea Tar Pits, in the ability to preserve fossils and give insight to the past, it is a true wonder and plethora of information.

            The history of the pits begins in tens of thousands of years ago, but the first recorded history of La Brea was by a Franciscan friar who accompanied Gaspar de Portola on a Spanish survey expedition. In 1769, during the expedition led by Portola, Father Juan Crespi noted in his diary that they came across “extensive swamps of bitumen”; he was the first person to use the term in describing these oddly indescribable pits but nowhere near the last. In 1828, a major event took place in that Antonio de Rocha, an ex-Portuguese sailor, became the owner of the tar springs via a land grant by the Mexican government. He was granted 4,439 acres, with the stipulation that he must allow the local inhabitants collection and use of the tar as needed. Although to that point there was no scientific reason for excavating the tar pits, Native Americans had been using the material for centuries prior for such things as waterproofing baskets, caulking canoes, and adhering of remedial tools. So, for practical use, the Spanish locals used the tar for various things, mostly to protect their adobe houses from the rain. Due to Spanish ownership, the Spanish word for tar (brea) was used in naming the Rocha estate, which became known as Rancho La Brea. The first geologist to examine the area was William P. Blake, who visited and noted the “accumulated bitumen” in 1853. Not long afterward, another geologist named J. D. Whitney, visited the site in 1865. However, although his focus was on the bituminous material, he took notice of the cattle and bird carcasses that had been at one point animals unfortunate of becoming trapped in the pits and most likely dying due to starvation or lack of water. Whitney however did not think that there may be more entrapped animals deeper in the pits existing of another time.

              It was ten years later, in 1875 when William Denton ventured to the pits to evaluate oil prospects, that he took notice to the fact that there were fossilized remains of ancient life. It was in a conversation with Henry Hancock (who had acquired the property from the Rocha family), that Denton was shown a large canine tooth. Having previous experience with saber-tooth tigers, he recognized the likeness. Although he wrote on his discovery, it took another 30 years and a different geologist for real interest in the subject to grow. In 1901, another geologist interested in oil prospects, a William W. Orcutt, gained permission to excavate and eventually after a painstaking four years collected a substantial fossil collection including the only complete skull of a saber-tooth tiger in the world. As time passed and interest in the fossils grew, excavation efforts grew as well, and before long the Hancock family gave exclusive excavation rights to the County of Los Angeles. They used everything from dynamite to pick axes to break the hard top layer and make it down to where the fossils lay. Although the tar pits provide superior fossilization, the preservation of the fossils was hampered due to the difficulty of retrieving them and several other factors such as a lack of precise instruments and environmental damage.


            Throughout the ages of excavation, many creatures were found in fossil form, ranging from the Columbian Mammoth to the simple water flea. Of the ample list of mammals found, some of the more interesting and popular ones include: Ancient Bison, American Camel, Saber-Toothed Cat, American Lion, llama, Columbian Mammoth, American Mastodon, Short-Faced Bear, Dire Wolf, as well as several varieties of ground sloth. Of course there is one mammal considered more of a rarity, and that is the Human. Of all the excavation done, there has only been one human found. The only remains of a human ever found were that of a Native American woman whose partial skeleton seems to date at approximately 9,000 B.P. Some birds have been found as well, including eagles, Teratornithidae, and vultures. Neither invertebrates nor plants were able to avoid the depths of La Brea, as scorpions, termites, and grasshoppers as well as sycamores and cedar trees have been found. Even reptiles, amphibians, and fish have been found. Famous for an excellent collection of fossils, these pits meant an unpleasant death for many animals and even plants unfortunate enough to be ensnared in the methane seeping asphalt substance.


Image:Dire Wolf.jpg

                        (Two Fossilized Remains of Dire Wolf)

            There are different theories as to why exactly there are so many fossils in the La Brea Tar Pits. The most commonly accepted theory that matches closest with the statistics is the entrapment theory, which states that over time unfortunate animals of prey would wander into the tar and become inevitably stuck. After realizing their plight, they would perhaps cry in distress in hopes of some form of help and in turn would attract animals of a predatory nature. The predators when coming upon the trapped animal would then be unable to resist the primal urge of an easy meal, and would then get themselves stuck in the same predicament as their prey. This theory explains why the ratio of carnivore to herbivore fossils are so drastically in favor (or lack of favor) of the carnivores. For mammals, 85% of all fossils are carnivores. Wolves outnumbered the other animals unbelievably, followed by tigers and coyotes. This too is explainable due to the fact that wolves hunt in packs, therefore it is entirely possible that one creature of prey could take several wolves with them into the depths of La Brea. The bird fossils found are 70% carnivores, with eagles leading in number followed by condors and vultures. Another theory that could explain why the remains of the animals are so scattered and why many bones cannot be found to complete the skeletal fossils, is that of a catastrophic flood. It might also help explain why for some of these species, which date as old as 38,000 years on the lower parts and 13,500 on some of the higher areas of excavation, it would require 24,000 years of Tar Pits without severe hardening. Yet, being composed of petroleum, it seems as though the surface should have eventually hardened, preventing more animals from sinking in. Both sides offer explanation to different facets of the same situation, both based on fact and speculation.

Image:USA tar bubble la brea CA.jpg

                        (Methane Gas Bubble Emerging at La Brea Tar Pits)

            Modern day excavation occurs during the summer at Pit 91, when the tar is the most liquid, and can be observed by the public. So interesting are the La Brea Tar Pits, from the vast ancient life that has been found, to the geology of the area, and even in the name. All that has been found proves as a testament to species that once roamed not just in far regions of the world but right here in North America. The intricacies of the underground are so interesting, where a four foot wide pit can envelop a multitude of species all much bigger than the entry whole itself. Even the name itself, The La Brea Tar Pits is interesting in that it is a pleonasm, for it is a repetition of two languages overlapping. It all stands for “The The Tar Tar Pits”, and “The The Tar Pits” are quite interesting indeed.


Works Cited

Harris, J.M. and Jefferson. 1985. Localities of the Pleistocene: The La Brea Tar Pits. 15 April 2007.

La Brea Tar Pits.13 April 2007. Wikipedia. 15 April 2007.

Messmore, Scott. La Brea Tar Pits. 11 Dec. 2006. All Around The Globe. 15 April 2007.

Mestel, Rosie. 01 April. 1993. Saber-Toothed Tales. 15 April 2007.

Weston, William. La Brea Tar Pits: An Introductory History. March 2002. CRS Quarterly. 15 April 2007.


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