A pit is a naturally formed or human-made hole in the ground. Sinkholes and pitted outwash plains are types of natural pits; borrow pits are work places from which soil has been “borrowed” for a building project. Large-scale pits are developed when land is mined to extract minerals or other materials, such as coal. The term can also refer to a surface formation containing prehistoric animal fossils. That is, the formation is a “pit” only in the sense that animal remains are forever trapped there. As fossil sites, tar pits deserve special mention, since in actuality they are not composed of tar but of a natural accumulation of tarlike bitumen at the surface of the Earth in which animal bones are preserved. Bitumen is a viscous or solid mixture of hydrocarbons and other substances distilled from petroleum that form asphalt, coal, and other materials. (Tar, narrowly, is residue created from the distillation of coal.) The La Brea Tar Pits in Hancock Park, Los Angeles, have produced one of the most extraordinary fossil collections in the world, containing the remains of thousands of animals from the Early Pleistocene epoch, some 2.5 million years ago, and even a more recent human fossil, the “La Brea woman.” Brea means “tar” in Spanish, so “The La Brea Tar Pits” literally means “The The Tar Tar Pits.” The pits actually contain a thick deposit of asphalt, the heaviest grade of petroleum, which is an excellent preservative as it saturates the bones and preserves the original organic matter.