The asphalt seeps of Rancho La Brea have been of interest since prehistoric times: Native Americans used the asphalt as a glue or caulk, and early Angelenos used it as a roofing material. Though the first recorded mention of the asphalt dates back to the 1760s, it wasn't until 1875 that the animal remains found in the seeps were recognized by Professor William Denton as fossils, and until 1908 when they were first featured in an academic publication written by J. C. Merriam (mentor to Chester Stock).
Soon thereafter, more and more paleontologists — amateurs and professionals alike — became interested in the asphaltic fossils. Los Angeles High School biology teacher James Z. Gilbert (link out to Gilbert images) began a large excavation project in 1909, under the banner of the Southern California Academy of Sciences. Rancho La Brea's long history of encouraging volunteerism in the young started with Gilbert; his excavation team largely consisted of his own students from Los Angeles High School. His finds laid the groundwork for the founding of the Los Angeles County Museum of History, Science, and Art, which is now the Natural History Museum of Los Angeles County. Gilbert's Academy collections were some of the first moved into the new Museum in 1911, and mounted skeletons from Rancho La Brea were among the first displays in the Museum when it opened in 1913.
Excavation at Rancho La Brea has continued, off and on, since the beginning of the twentieth century. Although much of the surrounding landscape has changed immensely, many of our fundamental excavation techniques have remained the same: bones are excavated using small hand tools and field data is recorded with pen and paper. . Even our measurement system has its roots in the grid system laid out by excavators in 1913. We supplement and support these techniques with new technology — electric lamps warm and soften the particularly dense asphalt of Project 23, digital cameras document day-to-day progress quickly and cheaply, and computerized databases allow us to search through collections with a modicum of ease — but we doubt if anything will ever replace hand tools, pen, paper, and elbow grease.
The Hancock family purchased Rancho La Brea in the 1870s and encouraged the scientific investigation of the fossil deposits. While the Hancock family mined the asphalt (to be used as far away as San Francisco) and later industriously drilled for oil, a few small scale excavations were made between 1901 and 1910. From 1912-1913 a larger scale excavation was conducted by the University of California at Berkeley. In 1913, the Los Angeles County Museum of History, Science, and Art — which later became the Natural History Museum of Los Angeles County — launched a two year excavation project that recovered a million fossil bones from 96 quarries or "pits." 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.
Led by L. E. Wyman, museum 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 that 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 became one of the more famous North American paleontologists in large part for his research, discoveries, and publications on the fossils of Rancho La Brea.
Fossils from Pit 3 range from 14,000 years to more than 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 upright only one meter below the original ground level (pictured at left). Now on display at the La Brea Tar Pits Museum, this tree is the largest single fossil from Rancho La Brea.
Pit 4 yielded more than 1000 fossil birds that have been dated from 15 to 35,000 years old. This excavation reached a depth of 25 feet. The excavation was subsequently filled in but asphalt continued to seep into this locality. Escaping methane gas forms large bubbles in the seeping asphalt that are readily viewable from the walkway
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 merged into a single deposit that was at least 13,000 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. A number of prehistoric artifacts were found in the vicinity of this excavation.
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.
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 between 14-18,000 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.
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 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.
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. That excavation continued for nearly 40 years and has still not yet been completed.