The first and foremost interest in the La Brea tar pits were for its paleontological potential. With such excavation for the fossil recovery, the geology housing the fossils was completely ignored, and it is only of late (1970's and on) that the geology of La Brea was taken into consideration. Once the general geology was determined, it dismissed some of the myths as to how the tar pits were formed, and gave clear evidence as to how the tar penetrates into the sediments and rocks.
There are layers of gravel, sand, and clay which were laid down by ancient streams or rivers. Faulting within the rocks below the La Brea area , have opened cracks where the heat and pressure within the earth, has forced the petroleum up through these cracks. This petroleum penetrates the permeable layers of sand and gravel within the earth. Some faults have produced fissures which carries the tar to the surface. The asphaltic substance pools at the surface and tends to stay in low-lying areas, such as stream beds or depressions in the landscape.