Rancho La Brea - Fossil Ecosystems of North America: A Guide to the Sites and their Extraordinary Biotas - page 251

jewellery, and as waterproofing for canoes
and roofing (Harris and Jefferson, 1985),
but the first record of these deposits was that
of the Spanish explorer Gaspar de Portolá,
who noted 'muchos pantamos de brea'
(extensive bogs of tar) in 1769. In 1792 José
Longinos Martínez recorded “ . . . twenty
springs of liquid petroleum” and “ . . . a
large lake of pitch ... in which bubbles or
blisters are constantly forming and
exploding” (Stock and Harris, 1992).
In 1828 the area became part of a
Mexican land grant known as Rancho
La Brea (which literally means 'the tar
ranch', although the term 'tar' is not
strictly accurate - the naturally occurring
bituminous substance derived from
petroleum is asphalt). During the
nineteenth century, and especially during
the 1860s and 1870s, the asphalt began to
be mined commercially for road
construction and during these operations
workers began to find bones, but
disregarded these as the remains of recent
animals which had become trapped in the
sticky bogs.
It was not until 1875, when the owner
of the ranch, Major Henry Hancock,
presented the tooth of a sabre-toothed
cat to William Denton of the Boston
Society of Natural History that the true
age of the fossils was appreciated. Denton
visited the area and collected further
specimens of horses and birds. No
further interest was shown, however, until
1901, when the Los Angeles geologist
WW Orcutt visited the area with a view to
oil production. His scientific excavations
between 1901 and 1905 produced
specimens of sabre-toothed cat, wolf, and
ground sloth which were passed to Dr
John C Merriam of the University of
California. Merriam realized the
importance of the deposit and excavated
between 1906 and 1913, but in that year
Captain G Allan Hancock, the son of
Henry Hancock, gave the County of
Los Angeles exclusive rights to excavation
(Harris and Jefferson, 1985). More than

750,000 bones were removed in the first
2 years and in 1915 Captain Hancock
donated the fossils to the Los Angeles
County Museum. At the same time the
ranch, later renamed Hancock Park, was
also donated to the museum for
preservation, research, and exhibition. In
1963 Hancock Park was declared a
National Natural Landmark ( 285 ) and in
1969 excavation resumed at Pit 91 in
order to recover some of the smaller
elements of the fauna and flora, such as
insects, mollusks, seeds, and pollen,
which had hitherto been ignored.
Excavation continues to the present day.
The name most associated with the
research of these deposits is that of Chester
Stock (1892-1950), who was a student of
John C Merriam and who joined some of
the early excavations at La Brea from 1913
onwards. He was associated with the
Los Angeles County Museum from 1918
until his death and published the first
comprehensive monograph of the La Brea
fossils (Stock, 1930), which had reached
its seventh edition by 1992 (Stock and
Harris, 1992).

S TRATIGRAPHIC SETTING AND
TAPHONOMY OF THE R ANCHO
L A B REA BIOTA
Most of the fossils excavated at Rancho La
Brea have been estimated by carbon-14
dating to be between 11,000 and 38,000
years old, which means that the sediments
in which they are buried were deposited
during the final stages of the Wisconsinan
glaciation, at the very end of the
Pleistocene Epoch ( 287 ). In terms of
the North American Land Mammal Ages,
the fauna belongs to the latter part of the
Rancholabrean Land Mammal Age, which
began 500,000 years ago, defined by the
first occurrence of bison in North
America.
Prior to the start of the Wisconsinan
glaciation, 100,000 years ago, this part of
California was submerged by an extended
Pacific Ocean. The fall in sea level at the