by Susan Couso
Geologists deal in big numbers. Their domain goes back to the Earth’s formation, about 454 billion years ago (454 Ga), plus or minus 50 million years. The designation 10 Ma, means, to a geologist, 10 million years ago. The ‘a’ is for the Latin ‘annus’, meaning ‘year’. It is also written as Mya, Myr, etc., they all mean the same thing. They also use Ka for ‘thousands of years, and Ga for billions of years.
So, while anthropologists, for example, may say 3,000 BCE (before Common Era), that’s just a ‘blip’ of time to a geologist. Humans, as we think of them, arrived on the scene from 200,000 – 300,000 years ago.
During the mid-Cretaceous, 65 Ma to 145 Ma, North America was split down the middle by a huge inland sea.
The sea extended from the Arctic Ocean down to the Gulf of Mexico and from the Rockies to the Appalachians. It was over 2,000 miles long and 600 miles wide, and up to 2,500 feet deep. It was big.
The western half of North America was named Laramidia, and the eastern half, Appalachia.
Through continued uplift, the mountains were built, and through climate changes and ongoing geological changes, the sea was mostly drained, and the country’s midsection became a great plain, trapping what was left of the inland sea.
To make a really long story short, things continued to move and dry until little was left of this great sea.
The Sierra Nevada Mountains were formed, drainage was cut off and the Great Basin trapped what was left of the water. This water was eventually divided again, by climate changes, and became Lake Bonneville, to the east, and Lake Lahontan, to the west. All that is left today of Lake Bonneville, is the Great Salt Lake in Utah.
We are mainly concerned with Lake Lahontan, which at one time covered much of Nevada, and portions of Oregon and California. Its remnants include, Honey Lake, Pyramid Lake and the Carson Sink.
The lake was named for a 17th Century French Baron, Louis de La Hontan, and no, he was never in the area. But he was admired by a geologist named Clarence King, who dubbed the lake with its unusual name.
The pluvial Pleistocene (Ice Age) lake reached its peak about 12,700 years ago. It encompassed about 8,500 square miles, and, at its deepest, today’s Pyramid Lake, was about 900′ deep. It was the largest pluvial lake in the northern hemisphere.
The lake’s size created a wave action which carved the mountains and created caves and terraces. By 9,000 years ago, it had dried up into many smaller bodies of water, and then, these lakes dried up into the playas, such as the Black Rock Desert.
A pluvial lake is subjected to the climate changes, as it relies entirely on rainfall to sustain it, and today, evapotranspiration is much greater than in the past. A pluvial lake fluctuates constantly, and today, you can see the tufa formation high on many desert sites, showing the ancient water lines. The area around Pyramid Lake is perfect for ‘tufa viewing’.
The high-point of Lake Lahontan coincides with the time that humans were thought to first arrive in the area, and archaeologists have made many exciting ‘finds’ near its former shorelines.
The Ice Age glaciers did not reach the area, but the effects of the cooler climate made things very different than it is today. For one thing, it was wetter.
The flora and fauna represented this climate, and remnants are often found of these extinct creatures.
Mammoths, giant ground sloths, camels, shrub oxen, horses, cheetahs, and other extinct mammals are known to have inhabited Nevada during this time.
The past is still discovered as people stumble on the remains of this lost era. Honey Lake has yielded Mammoth teeth, and the desert is covered with millions of small seashells, and fossil mollusk shells abound. Who knows what is left to find?
Today, in Pyramid Lake, the ancient Ice Age relic, the cui-ui fish, thrives.
Susanville sits right on the shore of the lake when it was at its highest. As you look down Main Street, you can look out onto the ancient Lake Lahontan as it was over 12,000 years ago. But watch out for that saber-toothed tiger!
