The Southern Sierra Nevada (aka the “East Side”) are truly a sight to behold. Mountains like Mt. Whitney, Mt. Tom, and Mt. Dana jut straight into the heavens thousands of feet above the surrounding flat valleys. Ask any skier where the “real mountains” in California are, and if they know what’s what, they’ll point you south on US395.
In terms of global mountain ranges, the Southern Sierra don’t quite measure up to the classic ranges of the world like the Alaska Range, or the Andes or the Himalayas. But in a bar fight, they would totally take the Northern Sierra, even though the Northern Sierra have the best ski resort in the universe – Squaw Valley USA International Mountain resort (home of the 1960 winter Olympics).
In the sub-field of geology called tectonic geomorphology, scientists study the ways in which mountain ranges are shaped and created. At the core of that discipline is the understanding that mountain ranges exist as a result of the interaction between the processes of uplift and erosion. Put simply – the tallest mountain ranges on Earth are places where the land has been or is still being uplifted by tectonic processes faster (or for more time) than erosion has whittled away at them.
The evolution of the Sierra Nevada is a complicated, episodic tale during which North America grew, shrunk, built up, got eroded down, got pulled apart, and occasionally had giant chunks of other continents and volcanic arc smooshed onto the side of it over the millenia. The land surface of Western North America looked much different than it does today, such as this image showing the paleogeography of the West in the mid to late Miocene 5-10 million years ago. The Northern Sierra are shown by the letter “A.”
The formation of the Great Basin via extension of the crust in west-central Nevada occurred about 17 million years ago though to ~9 million years ago. The ranges and valleys we see today in the Basin and Range province were formed around 5-6 million years ago. The granite core of the Sierra, the Sierra Nevada batholith, is the frozen, uplifted, and eroded innards of Cretaceous cordilleran volcanic island arcs, like what you would see deep inside the volcanoes of Japan today. These granite plutons formed around 115-87 million years ago (Schoenherr, 1995) as a result of the subduction and melting of the Farralon plate.
About 50 million years ago in the late Cretaceous to middle Eocene, the northern Sierra were uplifted much, much higher than their present elevation. Unfortunately for north Tahoe skiers, the uplift petered out and erosion started to take over, reducing the Sierra to what’s called an eroded penneplain. What relief that exists there today is largely the result of glaciers carving out the landscape. Uplift in the Southern Sierra has been much greater than that in the Northern Sierra, and has also been largely asymmetrical from east to west. In fact, the Southern Sierra continue to be uplifted via large earthquakes such as the Lone Pine ~M8.0 in 1872. The result of this uplift is the incredible relief found in the Southern Sierra.
Relief in the Southern Sierra ranges (distance from the tops of mountains to the bottoms of adjacent valleys) can be upwards of 9 to 10,000 feet. If you start off at the trailhead to hike Mt. Tom, you’ll begin your very long day at around 4-5,000 feet, topping out many hours later at 13,652 feet. The technical term for that is a “s%$@load” of vertical and very very tired legs will almost certainly be the result.
In the northern Sierras, relief is markedly less amazing. Squaw Valley is so mind-bendingly rad because it has a whopping 2,850 feet of vertical if you ski from the top of Granite Peak to the Chamois to sit at the bar and claim your amazingness while enjoying a cold beer. As far as ski areas go, that’s a lot for the US, but it’s not even in the same league as what you get if you drive three hours south on US395 and earn your turns.
Far to the northeast of California lies Jackson Hole, a valley bordered by the magnificent Teton mountains, which have around 7,000 feet of relief above the valley. One reader of this column pointed out the similarity in relief between the Tetons and the Owens Valley of California last week. The two do share similar origins – the same processes of uplift and erosion that created the Sierra Nevada were at work in Jackson Hole during the Laramide Orogeny, or period of mountain building. The rocks that comprise the Grand Teton are the same rocks that are found on the other side of the Teton fault deep below the sediment-filled Jackson Hole valley; vertical offset via faulting there is around 25,000 feet on the Teton Fault according to the Wyoming State Geological Survey. Back in California, modern relief in the Owens Valley is around 10,000 feet, with an additional 10,000 feet of buried glacial sediments filling the valley. The relief via uplift there is therefore in the same ballpark as the Tetons.
Unless things change markedly, the Southern Sierra will continue to be uplifted, growing higher and higher with each large earthquake. No such luck for us here in north Tahoe Sierra where erosion takes it s toll and lowers our mountains every year.
Thanks for reading, and please post your earth-science questions in the comments boxes below and I’ll pick one to answer for next week’s column!
Blakey, Robert C.1997. Geological Society of AmericaMeeting, Salt Lake City, Utah, Oct. 1997