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Wednesday, March 19, 2014
At a Westside subway excavation, plenty of bones (and more) to pick
An exploratory shaft dug to assess soil conditions for future stations and tunnels has burped up a bonanza of prehistoric swag.
Seventy feet below Wilshire Boulevard, cater-corner from the Los
Angeles County Museum of Art's street-lamp installation, fresh air
roaring from giant ventilation pipes dulled the sickly sweet smell of
Amid the clatter of
jackhammers and the whine of a mini-excavator, paleontologist Kim Scott
scouted the tarry muck for relics from a long-buried beach. She had
plenty of choices.
Major construction on the highly anticipated Westside subway
extension won't begin until next year, but an exploratory shaft dug at
the corner of Ogden Drive to assess soil conditions for future stations
and tunnels has burped up a bonanza of prehistoric swag. Officials had
anticipated encountering a substantial cache: The dig is near the La
Brea Tar Pits and features a sandy matrix with naturally occurring
asphalt — a fossil haven.
recovered mollusks, asphalt-saturated sand dollars, pieces of driftwood
and Monterey cypress cones. For Scott, the most exciting finds have been
a rock embedded with what appears to be part of a sea lion's mouth
(perhaps 2 million years old) and a non-fossilized 10-foot limb from a
digger pine tree that would look right at home today in Central
"Here on the Miracle Mile is where the best record of life from the
last great ice age in the world is found," said Scott, field and
laboratory director with Cogstone Resource Management, based in Orange.
In the shaft, she added, "you're walking along an ice age shoreline."
The former Rancho La Brea area of Hancock Park and environs indeed
features one of the world's premier paleontological troves. Over the
millenniums, petroleum from once massive underground oil fields oozed to
the surface, forming bogs that trapped and killed unwary animals and
then preserved their skeletons.
Evidence abounds at the tar pits and the George C. Page Museum, just
east of the exploratory shaft, where in the heart of urban Los Angeles
scientists have uncovered remnants of dire wolves, saber-toothed cats,
ground sloths and other species.
The swimming-pool-size shaft, 18 feet wide by 38 feet long, is
yielding evidence from its depths of a cooler, wetter Pleistocene
climate of 100,000 to 330,000 years ago, when Pacific Ocean waves lapped
over what is now the bustling Miracle Mile. Materials from the upper 40
feet of the shaft range from modern era to 50,000 years old. Below that
is "near shore" material from 100,000 to at least 330,000 years old,
John M. Harris, the Page's chief curator, said the area, though rich
in fossils, is nonetheless a finite source. "It's hit or miss," he said.
"Anything still in the ground is very important."
Although the area is protected, LACMA years ago was granted
dispensation to build an underground garage to replace an old May Co.
parking structure. In 2009, the Page announced the discovery three years
earlier of the largest known cache of fossils from the last ice age. In
one spectacular instance, a worker scraped his bulldozer across what
turned out to be a nearly intact skeleton of a Columbian mammoth with
10-foot-long tusks, which researchers named Zed.
Scientists reveled in the find, given that previous discoveries in
the tar pits had included only bits and pieces of mammoths. So that
construction could resume as quickly as possible, paleontologists
pioneered a process similar to that used to move large living trees.
After identifying the edges of each of 16 deposits, they dug around and
underneath them, wrapped them in heavy plastic, built wooden crates
around them and lifted them out with a heavy crane.
Similar discoveries are expected once excavation begins for the
Fairfax station, and scientists plan to use the same extraction method.
At this stage in the exploratory shaft, which will be twice as deep
as any other previous excavation in the area, the marine finds are quite
portable — geoducks, clams, snails, mussels, tusk shells. They're
collected in takeout-food containers made of plastic (so that the
asphalt does not stick). As for the rock that possibly contains a sea
lion's tooth root, Scott explained that it probably washed out of an old
formation and floated down a stream to the beach.
"Even though we're finding fossils older than what's found at La
Brea, none of the identified fossils found to date are extinct," Scott
said. "We can still find all the plants and animals in California."
Asphalt from an earlier descent already coated Scott's jeans, work
boots and right forearm when she headed back down the steep metal steps
into the hole one recent afternoon. The uneven surface at the base made
it tough to balance. She stepped back with one foot, which sank
immediately into ankle-deep water. Above the fresh muck, wood and
shotcrete had been installed to hold back the soil.
Two miners used jackhammers to dislodge ancient layers of sticky sand
mixed with silt, gravel and shells. The operator of the mini-excavator
shoveled the sludge to one side of the shaft, where it would later be
piled into a bin and hoisted to the surface to be loaded into a truck
headed for an Azusa landfill.
Bethany Ader, another Cogstone paleontologist, scrambled up and down a
slippery slope of tar sand carrying small relics. The two scientists
have routinely worked 15-hour days.
Work on the shaft began last April, and workers expect to hit 75 feet
by the end of March. They will then excavate an additional 2 feet to
pour a concrete slab floor, said Mark Bray, resident engineer. A water
pump in the floor will collect rainwater and any groundwater that enters
from "weep holes" built into the shotcrete.
Once the shaft is completed, it will be covered by street grating.
Over the next six months, engineers will enter the shaft periodically to
check for water and assess how the soils will react during the subway
tunneling and station construction.
Eventually, workers will spend about two months removing equipment
and backfilling the shaft with a mixture of cement and sand. At some
point years hence, commuters will walk through the subterranean station,
unaware that they're surrounded by the remnants of a distant sea.
"Here in Mid-Wilshire," said Dave Sotero, a Metro spokesman, "L.A.'s prehistoric past is meeting its subway future."