La Brea Tar Pits. Illustration of prehistoric animals becoming trapped in the La Brea Tar Pits during the Pleistocene. A dead mammoth is being scavenged by prehistoric sabre-toothed cats, vultures and wolves. Tar pits are areas where natural tar (asphalt) seeps from the ground. Animals that enter such tar pits often get stuck and die, with predators attempting to feed on the dead animals also getting stuck. The dead bodies then fossilise, allowing them to be excavated thousands of years later. These tar pits are in what is now Los Angeles, California, USA. The oldest fossils found here date from around 38,000 years ago. The most common specimens found here are from the Smilodon genus of sabre-toothed cats.