Rancho La Brea Early Excavations | Natural History Museum of Los Angeles

Excavators at work in Pit 67.

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Early Excavations

The Hancock family purchased Rancho La Brea in the 1870s and encouraged the scientific investigation of the fossil deposits. While the Hancock family industriously drilled for oil and mined the asphalt to be used as far away as San Francisco, a few small scale excavations were made. These were mainly conducted by the University of California, Berkeley, between 1901 and 1912. In 1913, the Los Angeles County Museum of History, Science, and Art — which later became the Natural History Museum of Los Angeles County — launched large scale excavations which lasted almost two years.

During these excavations a million fossilized bones were unearthed and cleaned from 96 quarries or "pits."  Led by L. E. Wyman, excavators earned $3.50 a day — decent wages for 1913 — but worked in terribly dangerous conditions. Shoring methods were primitive, and floods and cave-ins were common. In addition, the newly recovered bones were scrubbed clean of asphalt with heated kerosene and  caught fire from time to time. After this massive excavation and preparation effort, much of the ensuing scientific research on the newly discovered fossils was undertaken by Chester Stock. A graduate of the University of California, Berkeley, and a professor at the California Institute of Technology, Stock eventually became one of the more famous North American paleontologists for his research, discoveries, and publications on the fossils of Rancho La Brea.

The remains of several of these excavations are still on view to the public, including Pits 3, 4, 9, 13, 61, 67, and of course, Pit 91

Pits 3, 4, 61, and 67

Excavation of these four pits took place between July 16, 1913 and September 9, 1914.  These four deposits were located close together and today occupy the same swampy, fenced-in area southeast of Pit 91. Pits 3,4, 61, and 67 feature some of the most visibly active seeps in the park today; escaping methane gases form large bubbles on the asphalt seeps and are readily viewable from the walkway.

Pit 3

Carbon dates place upper levels of Pit 3 at 14,000 years old, whereas lower levels are around 20,000 years old. Though Pit 3 yielded over 500 mammal skulls, perhaps the most notable fossil from the deposit is that of a nearly complete juniper tree trunk, found only one meter below the original ground level (pictured at left).  Now on display at the Page Museum, this tree is the largest single fossil from Rancho La Brea.

Pit 4

Pit 4 yielded more than 1000 fossil birds and has been dated at 15 to 35,000 years old. Original excavation reached a depth of 25 feet.

Pits 61 and 67

Pits 61 and 67 originally started out as two separate excavations, but as they reached greater depths it became clear that they represented a single deposit that was approximately 12,000 years old. Hundreds of skulls were recovered from this deposit, and though bones from sabertoothed cats and dire wolves were most common, there are also many fossils of camels, bison, deer, horse, and ground sloths.

Pit 9

Pit 9 was excavated from November 18, 1913 to September 9, 1914 to a final depth of 35 feet. It is located immediately north of the Pit 91 compound. Over 10,000 fossils were recovered, including those from short-faced bear, American lion, mastodons, sabertoothed cats, dire wolves, camels, horses and ground sloth. Most notably, it is Rancho La Brea's main locality for Columbian mammoths. Over 30 individuals were recovered from Pit 9, ranging in age from very young to very mature. 

Left: A fossil assemblage from Pit 9, featuring the lower jaw of a bison on top of the lower jaw of a mammoth.

Pit 13

Pit 13 is located in the northwestern corner of Hancock Park, and was excavated from April 17 to September 24, 1914.  It was a conical deposit 9 feet in diameter and 23 feet deep, and bones from this excavation have been dated at 15,000 years old.  Notable finds include a large amount of ground sloth fossils, as well as over 100 skulls of other mammals. Also notable: bones from Pit 13 feature a large amount of pit wear — grooves and rivulets caused by bone-on-bone friction.

Pit 81

Early excavators were just as keen to show off their newly discovered treasures as we are today. They also recognized the importance of preserving fossil assemblages and understood the significance of cleaning and preparing fossils within a laboratory setting. Discovered in May 1915, Pit 81 was removed en bloc with the intention of putting the entire deposit on display at the Museum. On September 4, lead excavator L. E. Wyman wrote,

"North wall cracking badly, hence a heavy stull placed across pit to opposite wall.  Canvas removed and locality cleaned up generally. All ready for expert movers to do their work. Truck, with three men, four big mules, and all sorts of jacks, blocks and tackle, reached scene at 10.15 am, through the open field to the west. At 12.15 pm Pit No. 81 was on the truck and starting for the Museum, where the load was discharged at 4.30 pm."

The Pit 81 block (pictured at left in 1915, being loaded onto a mule cart) is now on display at the Page Museum. Nearly 100 years later, a similar boxing technique was used by paleomitigators for the Project 23 salvage.  


Pit 91

Excavation of Pit 91 began on June 13, 1915 and, like Pit 81, was slated to become a permanent exhibit. Wyman and his team originally excavated to a depth of 10 feet, and then planned on leaving the remaining exposed bones in place for park visitors to see. However, the site was never roofed, and eventually caved in. Fifty-four years later, paleontologists returned to Pit 91 to continue excavating.  More on Pit 91 >

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