Two weeks ago my
title was MOG: “Mother-of-the-Groom” in US wedding lingo. I was in Los Angeles,
California, to celebrate the wedding of my son, whose apartment is just a couple
blocks from the world-famous La Brea Tar Pits.
On the 1-mile walk from
our hotel to son’s apartment, I cut through Hancock Park,
which includes the campus of LACMA (Los Angeles County Museum of Art) and the Tar
Pits. I walked under Levitated Mass, a
large outdoor static-art piece (nod to any igneous geologists out there),
opened to the public in 2012*, and then ESE through the grounds of the adjacent
Tar Pits.
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| Levitated Mass in upper left corner, LACMA left and lower center, Tar Pits is green space. The large Lake Pit, with mammoth sculpture group, just to left of red pin; Project 23 boxes and exam space are little white dots in upper center (iPhone screen capture from Maps app). |
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| Levitated Mass by Michael Heizer. Top photo from LACMA website; bottom photo, and all others with no attribution in this blog post, by Malinconico. The art piece includes the rock mass, walkway, and surrounding decomposed granite aggregate. The big rock is a diorite, probably Cretaceous, from Stone Valley Quarry, an aggregate quarry in the Jurupa Mountains near Glen Avon, California*. |
Yes, people will tell
you that the name, La Brea Tar Pits, is a redundancy since La Brea means “tar” in
Spanish. Rancho La Brea was one of the original colonial Spanish land grants (http://www.tarpits.org/la-brea-tar-pits/timeline: History).
Oil seeps upward from the Salt Lake oil field, in the northern part of the Los
Angeles basin (http://www.searchanddiscovery.com/pdfz/documents/2012/20164gautier/ndx_gautier.pdf.html,
slide 6; http://www.ucmp.berkeley.edu/quaternary/labrea.php), and the loss of volatile hydrocarbons leaves
behind a tarry “gooey” residue AKA asphalt or bitumen.
Native Americans and
later European settlers had used the tar for mortar, glue, caulking,
medicine, and fuel.
These uses were also known 5000 years ago in the Middle East (Daniel Yergin, The Prize, 1991, p. 23-24). The Hancock
family, who owned Rancho La Brea in the late 19th/early 20th
centuries, initially mined the asphalt, but later went into oil production on
the land. Animal bones found in the La Brea tar were originally thought to be
those of modern cattle, but, in 1875, it was recognized that the bones were
actually fossils. Studies since have been “the core of late Pleistocene North American [paleontological] research”.
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| Excavating fossils 1913-15 at La Brea, Hancock Ranch, with oil wells in background (http://www.tarpits.org/la-brea-tar-pits/timeline: Excavations). |
The present-day La Brea ponds filled
with water and a scum of tar are remnants of former fossil (numbered on map) or
mined-asphalt (Lake Pit) excavation pits (http://www.tarpits.org/visit/map). Besides these pits, a large number of
tar-encased fossils are currently being “released” from Project 23: in 2006,
during construction of an underground parking garage for LACMA, new fossil
deposits were found. Twenty-three (therefore the name, Project 23) large wooden boxes were built around the
masses of asphalt, to preserve the relationship of bones to each other, and
removed, along with over 300 buckets of asphalt, for further examination. One can see remaining boxes outside on the
grounds (photos below) with preliminary examination workstations and a
blackboard describing the latest in what’s been found. Fossil exhibits,
laboratories and research facilities are in the Page Museum onsite.
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| Pit 13 |
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| Tarry scum on surface of water in Lake Pit |
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| Project 23 preliminary examination lab: Large wooden box, by blue wheelbarrow, is open, tent behind holds exam table space, other large boxes in background. |
The fossils found at La Brea
represent those from ~40,000 years ago (Late Pleistocene) into the Quaternary
(<11,700 years ago).
Quaternary fauna recovered are like those we live with today, but the Late
Pleistocene fossils include large extinct mammals such as mastodons, mammoths,
and the saber-toothed cats (http://www.tarpits.org/la-brea-tar-pits/timeline: Pleistocene).
Most of the recovered fossils are those of predators and scavengers, assumably
packs of predators chasing lone prey, all getting stuck in the tar (http://www.ucmp.berkeley.edu/quaternary/labrea.php). Several causes of the extinction at the end of the Pleistocene have been hypothesized. Climate change at
the end of the last (Wisconsin) Ice Age, overkill by early man, or a combination
of both are suggested.
A very controversial hypothesis was climate change caused by impact or low-atmosphere
explosion of a meteor over Canada (http://www.nature.com/news/evidence-found-for-planet-cooling-asteroid-1.13661
plus references for and against cited in linked PNAS paper and weblinks. I was never convinced of such an impact, and a 2023 open-access article in Earth-Science Reviews refutes that hypothesis.
I exited the Tar Pits by the large Lake Pit and its sculpture group of three Columbian mammoths: the mother tragically mired in tar, with panicked offspring and mate on the shore. The sorrowful scenario, although not fine art, is one of my three personal favorite emotive sculptures, the other two being The Dying Gaul and The Peace Monument, with Grief leaning on the shoulder of History.
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| Lake Pit with mammoth family and bubbling methane in foreground and to left behind mired mother. Page Museum is building in background |
After the wedding, we
drove to Las Vegas. On the north side of highway I-15 right before the California-Nevada state
line are the Mountain Pass rare-earth-element (REE) mine and
processing plant**. (At the time of this 2015 trip, Mountain Pass was owned by Molycorp, but the operation went bankrupt and was sold in 2017 [http://www.mining.com/mountain-pass-sells-20-5-million/]).The north rim of the open pit can be seen from the highway.
The ore body is the Sulphide Queen stock, a 1.4 billion-year-old carbonatite
(note a second igneous reference in this post!). Carbonatite is an igneous rock
with a large percent of carbonate minerals (so not the organic carbon of this
blog’s focus), which at Mountain Pass are primarily calcite, dolomite, and
barite. The REE-bearing ore mineral is bastnäsite. Uses for REE include
high-efficiency magnets in modern wind turbines and electric motors, and as
coatings in compact fluorescent light bulbs, all important technologies in both
saving energy and the transition to non-fossil fuel-based energy systems.
*Some Levitated Mass links about the sculpture, rock source and transport:
- http://collections.lacma.org/node/424258
- http://quarriesandbeyond.org/states/ca/quarry_photo/ca-riverside_photos.html (Scroll halfway down list of quarries to “Jurupa Valley, Riverside County, California – Stone Valley Quarry (Granite)”
- ftp://ftp.consrv.ca.gov/pub/dmg/pubs/sr/sr_23/Temescal_Valley_Rpt%20Final_11-04-14-a.pdf “The 40-acre area of the Stone Valley Quarry in the Jurupa Hills, north of the community of Glen Avon. This aggregate resource was originally identified in SR 165 as Aggregate Resource Area. The reserve and resource totals are proprietary.”
- http://www.kcet.org/arts/artbound/counties/riverside/levitating-the-archaic-mind-with-michael-heizers-levitated-mass-at-los-angeles-county-museum-of-art.html
Some background on project, finding the rock, plus fascinating photo of rock sitting alone in middle of quarry. - Summary video of installation of Levitated Mass including transport of rock to LACMA: https://www.youtube.com/watch?v=MD_6az-OI_A
Mine and processing plant (when owned by Molycorp):
Geology:
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