To simplify the story, the tar is a natural occurrence here. The animals walked through it, got trapped, died, and became preserved.
Their website has pictures and brief descriptions of the fossils found at Rancho La Brea. These include Sloths, Saber-Toothed Tigers, Bison, Dire Wolves and more. If you're looking for Dinosaur related info you should check out The Natural History Museum of Los Angeles instead. They have amazing fossils of various dinosaurs.
Go to the website and see if there is material that can be printed out.
Call the office i am sure they can send info however they specialize in Mammoth and othwr imals that were in the area
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