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Roger Weller, geology instructor

La Brea Tar Pits
by Kelsea Backinger
Historical Geology
Spring 2007

Ranchos La Brea Tar Pits

             Welcome to the Virtual Geology Museum!  You are about to embark on an adventure through the La Brea Tar Pits.  I hope you’re ready. Things can get pretty sticky!  Naturally occurring extensive bogs of tar continue to bubble as they did over 40,000 years ago.  This is not the first image that pops into your mind when you think of the booming Southern California city of Los Angels.  This phenomenon is the Ranchos La Brea Tar pits.  What actually created the industrial giant Los Angels was the immense asphalt deposits that were used as fuel, roofing tar, and petroleum to fuel heat.

George C. Page Museum, La Brea Tar Pits, Los Angeles, California
R.Weller/Cochise College

            For thousands of years, before L.A. emerged, local Chumsh and Gabrielino Indians inhabited the area.  Tar produced from the pits was primarily used as a glue, to bind broken pottery and objects together, also for fastening decorative shells on household items.  This sticky asphalt was also utilized to water proof baskets and seal canoes together.  It wasn’t until 1828 that a land grant over Ranchos La Brea began the exchange of tar for money.  Charging between 13 and 16 dollars per ton of tar began the explosive use of the pits.  The tar was used for roofing, and as years passed, the pits proved valuable for uses such as oil and petroleum.

            You are probably wondering, what caused the Earth to leak gasoline?  It all started over one-hundred thousand years ago while Los Angeles was home to a plethora of Pleistocene marine life.  In other words, it was under the Pacific Ocean.  Causing the ocean to retreat was the last glaciation of this era, thus exposing a plain of flat ground between the Santa Monica Mountains and the receding ocean.  Erosion of streams along the Hollywood hills initiated the accumulation of river deposits at the canyon mouth.  Los Angeles was much cooler and moister 40,000 years ago.  As time passed, those “alluvial fans” extended out over the plains.  Within the Earth’s crust movements of plates was causing faults, cracks, and fissures.  A layer of mud, sand, and gravel from the river’s extended into the Salt Lake Oil field natural reservoirs. 

            The cracks in the Earths’ surface began to discharge oil.  Sticky pools of shallow asphalt were left behind after light petroleum was evaporated.  These pools of tar became the sticky graves to many variations of wildlife from millions of years ago. Very important figures arise when it came to the preservation of the La Brea fossils.  Let’s take a look in our person’s involved vault.

            In 1875, Major Henry Hancock, owner of the Ranchos La Brea tar pits at the time, presented the first discovered Saber Tooth Cat canine tooth to Professor William Denton.  This created much excitement of what other mysterious bones were preserved in the pits. 

George C. Page Museum, La Brea Tar Pits, Los Angeles, California
R.Weller/Cochise College

            Captain G. Allan Hancock inherited the major portion of La Brea in 1913 from his parents.  Hancock was the person responsible for the preservation of the tar pits.  Encouraging interest of the Natural History Museum, Captain Hancock wanted these precious fossils to be studied and preserved. 

            Chester Stock contributed to the excavations on La Brea from 1912-1913.  Publishing the first ever research on fossil Ground Sloth’s, Stock was awarded his doctorate in 1917 due to these six self-written land-breaking studies.  Publicity and awareness of Ranchos La Brea can be complimented to Chester Stock for publishing the first comprehensive account of the fossils in 1930 to the general public.  In 1949, Stock was appointed Head of the Science Division, yet, passed away a year later.

Ground Sloth  Skull-George C. Page Museum, La Brea Tar Pits, Los Angeles, California
R.Weller/Cochise College

            George C. Page was the creator and constructer of the Page Museum of La Brea Discoveries in 1975.  The museum was opened to the public’s eager eyes on April 13th, 1977.  Page, was a pioneer developer to many of the nations first industrial parks.

            John C. Merriam specialized in Paleozoic invertebrates.  Most of Merriam’s research was carried out between 1900-1919.  Merriam’s most famous contribution to his vertebrate fossil study was from the La Brea Tar Pits.  Merriam and his students, most notably Chester Stock, described several species of vertebrates, most notorious of these bones was the Saber-Tooth Cat.  Merriam also identified wolves, bears, and peccaries.  

George C. Page Museum, La Brea Tar Pits, Los Angeles, California
R.Weller/Cochise College

            Fifty-five different species of mammals alone were founded out of over 1 million mammal fossils in the tar.  The asphalt deposits presented the numerous skeletons, creating a giant puzzle for geologists.  However, it wasn’t until 1901 that the first excavations of the tar pools was even carried out.  Oddly, 90% of the mammal fossils found represents carnivorous animals.  Scavengers and carnivores would see prey in the tar and go to eat it. Surprise! They become entrapped in the gooey tar also.  Another explanation for this phenomenon is that, often, predators hunt in packs, chasing a lone prey into the tar pit.  Unknowingly, they would follow the prey into the pits and all die in mass numbers.

Dire Wolf Skulls-George C. Page Museum, La Brea Tar Pits, Los Angeles, California
R.Weller/Cochise College


            The most common fossil in the tar pits is the Dire Wolf.  This mammal was similar in size to the modern grey wolf.  Large teeth, massive jaws, and proportionally small legs gave the Dire wolf a specialized body for hunting prey.  The Dire wolf was built for stealth.  It was during that last Ice Age that Dire Wolves hunted the lands of Ranchos La Brea.  The extensive amount of Dire Wolf fossils in the asphalt pits is due to the fact that these fierce predators hunted in packs-causing them to die in the tars pits at the same time.  The picture below is that of a Dire Wolf skeleton from La Brea.


Dire Wolf -George C. Page Museum, La Brea Tar Pits, Los Angeles, California

R.Weller/Cochise College


            It is hard to image camels living in California. The now extinct American Camel appeared at La Brea centuries ago.  There were to species of camels that appeared at the pit.  Camelops Hesternus, the larger more commonly found species was over 10 feet tall at the shoulder. This camel is closely related to our present day camel, except it had longer legs, and some may have lacked humps.  The second species of camel was Hemiachenia macrolephala, being 1/3 larger than lamas today, Hemiachenia macrolephala extinct long ago, thankfully for out modern llamas!!!!

            Saber-Toothed Cats, other known as Smilodon californicus are the second most common fossil at La Brea, aside from the Dire Wolfs.  The Saber Cat was slightly larger than the size of today’s modern African Lion.  The Saber tooth cat used ambush tactics to acquire their prey.  The most interesting aspect of the saber-tooth cat is its impressive set of upper-canine teeth.  These gigantic teeth were though too been used to gouge into the soft underbelly of their prey.  Saber Tooth Cats are believed to have hunted in packs.  First appearing in the Eocene epoch, Saber Cats have given rise to true cats during Pliocene epoch.  The figure below is actually a façade to the Saber Tooth Cats at Ranchos La Brea.  Check it out!


Facade of the George C. Page Museum, La Brea Tar Pits, Los Angeles, California
R.Weller/Cochise College


            Standing Four feet ten inches at the shoulder, the Western Horse was as tall as the modern Arabian horses, just more heavily built.  Western Horses became extinct in North America at the end of the Pliocene epoch.  They were later re-introduced in Europe and were one of the last species of horse native to North America.

            The largest of all elephants to live in North America, the Imperial Mammoth.  Some of these impressive creates grew to reach 13 feet tall!  On the average weighing in at 10,000 Lbs. These mammoths came to being at the beginning of the Miocene Epoch.  Mammoths and elephants are alike; however, their trunks differed in shape.  Mammoths had developed a thick coat to keep them warm during the Ice Age.

George C. Page Museum, La Brea Tar Pits, Los Angeles, California
R.Weller/Cochise College

            Today, when we hear the term “sloth” envisions an image of a 3 toed-sloth hanging from a tree in the Amazon come to mind.  Picture a sloth that weighed an estimated 3,500 Lbs. and stood six-feet tall?  That my friend is the Harlan's Ground Sloth.  Although this may sound like a scary beast, it was a herbivore, and preferred an all grass diet. Below is a picture of a giant ground sloth skeleton.  This is a display at George C. Page Museum, Los Angeles.


Ground Sloth-George C. Page Museum, La Brea Tar Pits, Los Angeles, California

R.Weller/Cochise College


            Tapirs are often distinguished for their beautiful patterned fur.  The tapirs found in La Brea are hypnotized to look very similar.  The tapirs had low-crowned teeth for browsing on leaves and other vegetation.  The proboscis on the tapir acts like a mini “trunk” for pushing food into the orifice.  Tapirs are distant relatives to horses.  Both of these species were widespread about North America during the Pliocene era.  This led to evolutionary similarities and differences.  However, evidence of Tapir’s in La Brea is minimal, yet fascinating!    

            I hope you enjoyed your adventure through Ranchos La Brea today!  There are a plethora diverse species at the tar pits aside from the animal described above, for instance, fossils of varies birds, reptiles, invertebrates, carnivores and other mammal remains are found  in the L.A. tar!  I hope you enjoyed your trip at the Ranchos La Brea exhibit, and have fun viewing the rest of the Virtual Geology Museum.



Works Cited


Harris, John M. Jefferson George T.1985  Rancho La Brea: Treasures of the Tar Pits. Natural History Museum of Los Angeles County.
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LaBrea Tarpits.
Copyright 2001-2007

Weller, R./Cochise College.
Photos of the George C. Page Museum