Many theories were developed about how these animals could have become trapped. The theory which has stood out, and been accepted as the best explanation, assumes that the areas which contained the tar pools, were covered by sediment, leaves or water, thus disguising the trap. Any animals wandering over the tar could potentially become trapped.
If the tar pits were not covered, one would wonder: Why would these animals cross over the tar pits??
animals passing by La Brea were thought to be migratory; as they made their
bi-annual migrations, predators would use the La Brea area as traps for
their prey. Predators like the Saber-toothed cat, American lion, and Dire
wolf would push their prey through the tar pits in the hopes of one getting
stuck or slowed down. It is believed that the summer's heat would make
the asphalt a liquid or more "gooey", while at night, with cooler
temperatures, the tar would solidify anything stuck within it.