How were the Tar Pits Formed?
In the case of the La Brea Tar Pits, the area was underneath the Pacific Ocean for millions of years. During this time marine sedimentary layers formed and became rich with fossil fuels produced from ancient sea creatures. About 100,000 years ago, when sea level dropped, the area at La Brea became exposed as land. At this time, the oil-rich sediment was covered with new sand, gravel and clay. For the last 40,000 years oil has been seeping out of the ground, and has provided us with many excellent specimens from the Pleistocene.