The haul includes a near-intact mammoth skeleton, a skull of an American lion and the bones of saber-toothed cats, dire wolves, bison, horses, ground sloths and other mammals.
The remains were located near the famous La Brea Tar Pits in the Miracle Mile district of America's second-largest city.
Scientist Shelley M. Cox stands alongside the lower jawbone section of the mammoth skeleton, part of a haul of fossils found in central Los AngelesResearchers discovered the 16 fossil deposits in 2006 and began sifting through them last summer.
Archaeologist Robin Turner, who has previously overseen work on other sites at or near the tar pits, said the fossils were found 10ft below the surface.
'I knew we would find fossils but I never expected to find so many deposits,' he said. 'There was an absolutely remarkable quantity and quality.'
The mammoth desposits, including 10ft-long tusks, were in an ancient riverbed near the fossil cache.
Officials at the Page Museum at the tar pits plan to formally announce their findings today. The discoveries could double the museum's Ice Age collection.
Such a rich find usually takes years to excavate. But with a deadline looming to build an underground car park for the art museum next door, researchers boxed up the deposits and lifted them out of the ground using a crane.
Delicate procedure: Scientists brush away the dirt around the mammoth's pelvis. The mammoth has been nicknamed Zed
The haul of fossils were found beneath the car park of the old May Company building on Wilshire Boulevard and Fairfax'It's like a paleontological Christmas,' research team member Andie Thomer wrote in a blog post in July.
The research is dubbed Project 23 because it took 23 boxes to house the deposits. It has uncovered fossilised mammals as well as smaller animals including turtles, snails and insects.
Separately, scientists found a well-preserved Columbian mammoth that they nicknamed Zed.
An examination reveals Zed, which is 80 per cent complete, had arthritic joints and several broken and re-healed ribs - an indication that he suffered a major injury during his life.
'It's looking more and more as if Zed lived a pretty rough life,' Thomer blogged in December.
Fossil hunt: Excavator Kristen Brown carefully searches for remains in a crate of earth taken from the siteSome scientists not connected with the discovery said this is the first significant fossil find since the original excavations at the tar pits more than a century ago.
'Usually these things are either lost in the mixing or not recovered in the processing of the oily sand and soil they occur in,' paleontologist Jere H. Lipps of the University of California, Berkeley, said.
The La Brea Tar Pits ranks among the world's most famous fossil sites.
Between 10,000 and 40,000 years ago, mammoths, mastodons, saber-tooth cats and other Ice Age beasts became trapped by sticky asphalt oozing upward through cracks and fissures in the ground. The newly recovered fossils were also in asphalt.
Since 1906, more than a million bones have been unearthed from the sticky ponds.