Pit 91

One of the world’s longest-running urban paleontological excavation sites.

Pit 91

General Info

Open daily 9:30 am to 5 pm
Free with museum admission
Free for Members

Watch our excavators at work

Look down into an active fossil dig where scientists are uncovering everything from small plant sees to giant ground sloths. From the Viewing Station, you can see deep into Pit 91 where thousands of bones of extinct animals like the western horse, saber-tooth cat, and dire wolf are jumbled together in pools of sticky asphalt. Throughout the summer, watch real paleontologist excavate real fossils from the gloopy, black asphalt and learn how scientists use these specimens to study what Los Angeles was like 25,000 years ago during the Ice Age. Science happens daily here at La Brea Tar Pits, so there is always something new to discover.

Photography of man with gloved hands entirely covered in "tar"
excavation in pit 91
women in pit 91 field school la brea tar pits
fossil preparators excavation pit 91 la brea tar pits
Photograph of "tar" being poured from a bucket
Photograph of fossil preparators sitting in Pit 91

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The story of Pit 91

Pit 91 wasn’t always a pit. Thousands of years ago, during the Ice Age, it was a shallow pool of sticky asphalt that trapped and preserved all kinds of plants and animals that got too close. Over a long time, dirt and sand washed over the pool, burying it, and the fossils stuck there, underground. Paleontologists discovered and started excavating Pit 91 in 1915over a hundred years ago! The deposit is so rich in fossils that they still dig here every summer.

Early excavations focused on the bones of large mammals like giant ground sloths and saber-toothed cats but recently, paleontologists have been collecting microfossils, the tiny remains of plants and animals like seeds, twigs, snake bones, bird beaks, insect exoskeletons, and fish teeth. Digging at Pit 91 nearly doubled the number of species known from the Tar Pits and provided important data for understanding how climate change affected the habitat here. Pit 91 was the 91st hole dug by early paleontologists but when it comes to reconstructing ancient Ice Age ecosystems, it’s definitely Number 1.

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