New evidence acquired from an ongoing excavation project at Rancho La Brea has led to a major re-evaluation of how the fossils were deposited. The traditional idea that animals were trapped in continuously active, open pools of tar has been discarded, and new theories of entrapment and deposition emerged. Although more realistic in some ways than the old theory, the alternatives suffer from the same inability to provide a defendable, gradualistic explanation. This critique represents a preparatory stage in the development of a theory that discards the principle of animal entrapments and advances the concept of a diluvial process in the formation of the tar pit fossil beds.