The study of trilobites takes us to the start of the Phanerzoic eon 600 million
to about 230 million years ago. The Cryptozoic eon preceded this eon but so little
is known or in fact even remaining of that eon there is little left to study.
The Phanerozoic eon is divided into three eras, the earliest of which is known
as the Paleozoic era. This Paleozoic era then in turn is divided into six periods,
the first of which, the Cambrian, (600-500 million years ago), was the age in which
trilobites first put in an appearance. During the Ordovician or second period (500-
425 million years ago), the trilobites were most abundant. The Silurian period (425-
405 million years ago), saw the trilobites becoming less numerous but more
complicated in structure. The Devonian period (405-345 million years ago), and the
Carboniferous period (345-280 million years ago), found the trilobites decreasing in
population and finally during the Permian period (280-230 million years ago),
trilobites were at last becoming extinct. All this took place before the dinosaurs spent
their million years on earth.
"Trilobite" refers to the three lobes or sections into which these creatures
were divided - head, thorax and abdomen. The thorax region was divided into
segments with each segment bearing a pair of legs. Because the abdomen segment was
a much softer material most of the imprints found in the Marble Mountains of the
Mojave Desert show just the head and thorax parts. These trilobites, Paedumias
mohavensis, were the first of their kind, a spike-tailed, spiny-sided creature about
three inches long. Later models obtained a length of 18 inches, however.
An interesting abandoned mining operation is located adjacent to the site of
the trilobites. In 1937 a deposit of Calevanto Marble was discovered here and for
the next two years some 2,000 cubic feet of the highly colored material was cut
from this quarry by the Vaughan Marble Company. The Post Offices in Gardena and
Oxnard used this cut and polished marble as did the Custom House and the United
States Mint in San Francisco.
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