Location and formation La Brea Tar Pits

illustration of several species getting mired in tar pits

the la brea tar pits , hancock park situated within once mexican land grant of rancho la brea, part of urban los angeles in miracle mile district, adjacent los angeles county museum of art , craft , folk art museum.

the tar pits visible today human excavation. lake pit asphalt mine. other pits visible today produced between 1913 , 1915, when on 100 pits excavated in search of large mammal bones. various combinations of asphaltum , waggler have since filled in these holes. normally, asphalt appears in vents, hardening oozes out, form stubby mounds. these can seen in several areas of park.

tar pits composed of heavy oil fractions called gilsonite, seeped earth oil. in hancock park, crude oil seeps along 6th street fault salt lake oil field, underlies of fairfax district north of park. oil reaches surface , forms pools @ several locations in park, becoming asphalt lighter fractions of petroleum biodegrade or evaporate.

this seepage has been happening tens of thousands of years. time time, asphalt form deposit thick enough trap animals, , surface covered layers of water, dust, or leaves. animals wander in, become trapped, , die. predators enter eat trapped animals , become stuck.

as bones of dead animals sink asphalt, soaks them, turning them dark-brown or black color. lighter fractions of petroleum evaporate asphalt, leaving more solid substance, encases bones. dramatic fossils of large mammals have been extricated tar, asphalt preserves microfossils: wood , plant remnants, rodent bones, insects, mollusks, dust, seeds, leaves, , pollen grains. examples of of these on display in george c. page museum. radiometric dating of preserved wood , bones has given age of 38,000 years oldest known material la brea seeps. pits still ensnare organisms today, of pits fenced protect humans , animals.