Fossils in Southern California
The earliest fossils known in Southern California are found in
the Kingston Range of the far northeastern Mojave Desert. The
fossils represent microbial life forms and may date from Proterozoic
times, as old as 1.5 billion years. During the Proterozoic, western
North America was covered by ocean waters: fossils of ocean-dwelling
organisms include trilobites (found in the Marble Mountains of
San Bernardino County), ammonoids, corals, and other plant and
invertebrate life forms.
During the Mesozoic Era- the Age of Dinosaurs-Southern California
was an island arc with offshore volcanoes The earliest evidence
of dinosaurs in California is in Early Jurassic dune sands along
the eastern shore of an sea near today's Nevada border, where
the only dinosaur tracks known in California are found. The remains
of hadrosaurs ("duck-billed" dinosaurs) occur along the coast
of California from San Francisco south to San Diego. A nodosaur,
built like a tank and protected by thick armor, was found in San
Diego. Fossils of plesiosaurs (huge swimming reptiles) have been
found in Cajon Pass, north of San Bernardino.
From 65 million to 3 million years ago, Southern California was
a vast, well-watered plain. Mammals flourished in tremendous variety:
camels, rhinoceros, giant bear-dogs, primitive elephants, early
saber-toothed cats, and giraffe-like chalicotheres roamed
the land. Notable occurrences of these fossils are found in the
Barstow Fossil Beds and in Cajon Pass.
During the past 3 million years, the San Bernardino Mountains
were uplifted along the San Andreas Fault. These mountains created
a barrier that changed weather patterns, resulting in today's
Mojave Desert. This period is colloquially called the "Ice Ages."
Southern California in the Ice Ages had abundant animals such
as saber-toothed cats, mastodons, mammoths, horses, giant camels,
and ground sloths. Ice Age fossils are found throughout Southern
California, including the "tar pits" at rancho La Brea and Diamond
Valley Lake near Hemet.