From The Animals of La Brea Tar Pits by Kit Winston.
"A mammoth may have walked into the sticky pools to get a drink, and then the enormous animal would sink, becoming partly submerged. The unfortunate mammoth may have sounded its mighty trunk, and that would have alerted meat-eating animals to a meal. A saber-toothed tiger may have heard the cries and, thinking that dinner was nearby, would have run to the tar pit. As the cat waded into the pit, it too would get stuck."