Tuesday, July 20, 2021

The Other California: What to See When You've Run Out of Postcard Destinations (Reprise)

(published by Scope Enterprises, Inc)
My earliest blog project was an exploration of the geologically interesting places in California that don't always show up on the postcards (the earliest post is here). I've been working on this project off and on for a dozen years. If you've followed my blog at all, you know I have a type of Geologist Attention Deficit Disorder Syndrome (GADDS), that as soon as I start concentrating on one subject, something interesting pops up somewhere else, and I explore it for a few weeks, and then get distracted again.

Geologists divide California into eleven geomorphic provinces, areas that share unique geologic histories, rock types and topography that are distinct from the surrounding areas. I generally refer to the province when I am describing a particular feature or place. I am categorizing the posts that exist thus far in the same way:
THE INTRODUCTION
The Other California: The Things it is Not: the first post describing what I am up to with this series: most people know about Yosemite, Sequoia, Death Valley and other famous places, but California has so much more...things and places that don't appear on the postcards
The Other California: Now This is a Postcard!: A brief overview of the geology of the state as it is represented on geologic maps and and introduction to the idea of provinces.
Come to California and You Could Die a Fiery Death! : A short introduction to volcanism in California

THE STATE SYMBOLS
Although the original idea came with a post about California's prairie lands, I pretty much first started out by describing the geologic significance of some of our state symbols.

The Other California: Already Off on a Tangent: A review of the familiar symbols, the Golden Poppy, the California Quail, the California Grizzly Bear, and our state mineral, Gold!
The Other California: Geology and our Other State Symbols: A look at the state mineral, the state rock, and the state gemstone, the one hardly anyone has heard of.
The Other California: Geology and our State Symbols Part 1: a discussion of the evolutionary history of our state fish, the Golden Trout
The Other California: Geology and the other State Symbols II: the incredible journey of our two state trees, the Sequoia and Coast Redwood
The Other California: Geology and the other State Symbols III: a look at our state fossil, the saber-tooth cat Smilodon Californicus.
The Other California: Geology and the other State Symbols IV: California has some unique Gold Rush-era towns, but nothing is quite like Bodie, off in the high desert east of the Sierra Nevada.
The Other California: Geology and the other State Symbols V : The strange politics that led to the establishment of the official California Silver-Rush Ghost Town.
Say Hello to California's New State Dinosaur, Augustynolophus morrisi: The first dinosaur discovered in California was found in our county, Stanislaus.

THE GREAT VALLEY
A huge 400 mile long valley filled with thousands of feet of sediments deposited over 160 million years, and one of the most fertile agricultural regions in the world

The Prairie Lands: California has its own version of savannahs, both present and past.
The Prairies of the Past: An exploration of the most important Pleistocene fossil quarry in central California, the Fairmead Landfill
The Prairie Lands and a Transforming Fault: A journey through Carrizo Plains National Monument and the best exposures of the San Andreas fault to be found anywhere
Back on the Prairielands: A springtime return to the prairies, now green and full of life
Mammoths and Sabertooths rise from the Prairies Again!: The Madera Fossil Discovery Center was almost complete and expected to open in June. Here is a preliminary look
Sharktooth Hill: That's about it...thousands and thousands of shark teeth and a great many other species. 

THE SIERRA NEVADA
The Sierra Nevada is the largest single mountain range in the United States, more than 400 miles long and averaging 50 miles wide. It also has the highest peak in the lower 48 states. Although composed mostly of granite, it also has large exposures of metamorphic and volcanic rocks that tell a remarkable story of traveling continents and terranes, as well as tales of violent eruptions.

A Gorge Deeper than the Grand Canyon: An exploration of little-known Pine Creek on the east side of the Sierra Nevada, and one of the most important mines in the country
The Other Yosemite at Hetch Hetchy: There was a counterpart to the Yosemite Valley, but we dammed it.
The Other Side of the Sierra, down the West Walker River: The West Walker River flows down the east side of the Sierra, and hosted the longest glaciers to be found on that side of the mountains.
An Enigmatic Gorge, the West Walker River Canyon: A strange entombed forest, and a deep gorge with a violent geologic temper.
The Day of the Fiddlenecks (A Trip Through the Mother Lode): A brief foray for wildflowers on Highway 132 in California's Mother Lode
There's an Endemic in those Red Hills! Life and evolution on one of California's unique environments, the serpentine soils. Exploring the Red Hills Area of Critical Environmental Concern
The California State Mineral Exhibit-This is art, darnit! One of the best ways to see the incredible mineral wealth of California is to explore the state mineral exhibit in Mariposa at the south end of the Mother Lode. Because of the morons in the state legislature, it is about to shutter its doors
It's a Real Grind...Chaw'se State Historical Park: A look at more grinding mortars than you'll ever see anywhere else, the Miwok culture, and some interesting metamorphic rocks
The Other California Goes Underground: Hella Hot Helictites at Black Chasm Cave: Never heard of helictites? That's because they are the first cave features to be destroyed. But we have a world class collection of them in the Sierra foothills
What do you do with a Used Forest?: The Sierra Nevada between Yosemite and Kings Canyon National Parks is terra incognita for most Sierra travelers. The region has been logged, mined, and grazed...and is still spectacular. We take an excursion on the Sierra Vista Scenic Byway
Why Worry About Yellowstone? We've got our own "supervolcanoes" in California. Some are active. Some have been extinct for tens of millions of years. At the Minarets we can explore one from the inside out


THE CASCADE RANGE
The Cascadia Subduction Zone is a place of geological violence: The crust underlying the Pacific Ocean is sinking beneath the western edge of the North American Continent, producing earthquakes, mountain-building, and volcanism. Two of California's most familiar volcanoes formed here, and the largest volcano in the state sits astride the boundary with the Modoc Plateau

Exploring California's Biggest Volcano: An introduction to the Medicine Lake Highland, one of California's most active volcanoes.
Geologists Who Live on Glass Mountains Shouldn't....: Looking at volcanic glass, obsidian and pumice, on the Medicine Lake Highland, with a view towards the Modoc Plateau, too.
A Land of Fire and Ice (but mostly ice): California's largest glaciers
Five For the Price of One: California's most prominent volcano is really five volcanoes, with a violent past.
A Monday Mystery: A river that comes out of nowhere, and a gratuitous picture of a deer family
A Mystery Solved, and One of California's Prettiest Little Waterfalls: McArthur Burney Falls is California's second oldest park, and is one unusual waterfall.
Lassen Peak, A Volcanic Afterthought: A well-known volcano that sits on the remains of a much older, much larger volcano, Mt. Tehama
Getting all excited about natural disasters: an eyewitness account of some of the events surrounding the 1914-15 eruption of Lassen Peak.

THE MODOC PLATEAU
The Modoc Plateau is a high flat region underlain by thick flows of basalt lavas in the remote northeast corner of the state. It is one of the least-known areas of California, but has some nice geological surprises.

California's Biggest Volcano: here is the first surprise; the biggest volcano is not named Shasta or Lassen!
Waiter, There's A'a in My Pahoehoe!: A comparison of basalt lava flows at Lava Beds National Monument
The Volcano Underground: the formation of lava tubes (via a short excursion in Hawaii) and Lava Beds National Monument
Exploring the Volcano Underground: Walking and crawling through the most extensive lava tube system in the continental United States
Whispers From the Past: Huge explosions from 270,000 years ago, and the largest petroglyph panel in the United States
Cries From the Past: A tale of rebellion, resilience and betrayal; the Modoc Indian War of 1872-73. And why armies should study geology before fighting wars.

THE KLAMATH MOUNTAINS
In northwest California, a series of mountain ridges reveal stories of continental and oceanic fragments that were crushed into the western edge of North America. The rocks bear a close resemblence to the Sierra Nevada, although they are offset more than sixty miles.

Flotsam and Jetsam: An introduction to the Klamath Mountains as a series of accreted terranes, tracts of crust and old ocean floor that traveled hundreds or thousands of miles.
Havin' fun with Sasquatch: a discussion of the legendary and mythological creature that supposedly dwells in the Klamaths
I've seen these mountains before! The Big Ripoff: Viewed on a geologic map, the Klamath Mountains look like a continuation of the Sierra Nevada, but lie sixty miles farther west.
A Journey to the Center of the Earth (sort of): A review of the some of the rocks from the deep crust and mantle that are found in the terranes of the Klamath Mountains
Taking Stock of Castle Crags: One of the most imposing sights (besides Shasta) to be seen on a journey north on Interstate 5, the Castle Crags are towers and domes of granite, surrounded by more easily eroded metamorphic rocks
THE COAST RANGES
The series of mountain ranges that roughly parallel California's coastline are one of most diverse areas of the state from a geologic standpoint. There are thick sequences of sedimentary rocks including the Great Valley Group and elements of the Franciscan Complex, and there are plutonic and metamorphic rocks of the Salinian Block (and parts of the Franciscan). There are even volcanic rocks and potentially active volcanoes.

I Need This Like I Need a Hole in the Head: Scenic Bodega Head at Bodega Bay was the nearly the site of one of the most mind-bogglingly stupid energy developments ever conceived by the minds of engineers
Baymouth Bars - It's Five O'Clock Somewhere? Along the incredibly rugged north coast amid the violent surf there are long, perfectly straight sand bars that seem to defy explanation. They're explained here Humboldt Lagoons State Park
A Mystery Photo For a Saturday: A look at San Francisco from a unique angle, Monte del Diablo
The Thicket of the Devil (the mystery photo revealed): An introduction to a place with an incredible view, Mt. Diablo. How it got its name and why every landowner in Central California should care
Limekiln State Park Part 1, Part 2, and Part 3: Limekiln is a beautiful gem of a state park on the Big Sur Coastline. Unfortunately we have morons in the state legislature and this park is closing. See what is being taken from us (PS: It was eventually saved)


BASIN AND RANGE
The crust of the earth east of the Sierra Nevada and Peninsular Ranges is being torn apart by horizontal extensional forces that have produced an alien landscape of deep fault valleys (grabens) and high mountain fault blocks (horsts)

The West Walker River and the Antelope Valley: A deep fault valley becomes an important ranching and farming region
Dammed if we do Dam, Dammed if we don't Dam: An unusual reservoir without a dam, Topaz Lake stores Walker River water, but has great fishing too. Why is it there?
Damned if we do Dam, Damned if we don't Dam: A slightly modified name, and a much bigger issue - What are we going to do about Walker Lake? It's dying. It's also in Nevada, but it is a California river.

MOJAVE DESERT
Often ignored or tolerated by tourists on their way to Las Vegas, the Mojave Desert is one of the most geologically diverse regions of California

The Calico Mountains: An exploration of a unique mountain range, well beyond the confines of the tourist trap ghost town.
Prairies past and Some Great Folds: A closer look at a parking lot in a tourist trap
A Wandering Volcano and a Floral Outburst: The Antelope Valley has a springtime show of wildflowers that is simply audacious, and the underlying rocks include half of a volcano. The other half is nearly 200 miles away...
Caught in the Vise (the Western Mojave Desert): A discussion of complex fault relationships in the western Mojave and another chance to show some wildflower shots.

COLORADO DESERT

THE TRANSVERSE RANGES
A diverse series of mountain ranges that run against the grain, trending east-west instead of north-south. These include some of the highest mountains in southern California

The Other California: A Friday Fun Foto: A first glance at San Gorgonio Peak, the highest mountain in southern California, and the southwesternmost glaciated peak in the United States
Scarps to the Left of Me, Sag Ponds to the right, Here I am, Stuck in the Middle with You!: The San Andreas fault cuts across many of California's province. In this post we look at some fault features at the top of the Grapevine in the Transverse Ranges
A Monday Mystery Photo: A quick introduction to the Cajon Pass country where the San Andreas fault splits the San Gabriel Mountains from the San Bernardino Mountains
Cajon Pass and No Strange Sci-Fi Creatures: Cajon Pass, the major freeway access route into the Los Angeles basin, is filled with strange looking sedimentary rocks tilted this way and that. But it's not where Captain Kirk fought the Gorn...
The Mountains of My Youth: The eastern San Gabriel Mountains aren't all that familiar to people from outside the state, but they are spectacular and they were the mountains where I grew up. We explore an extraordinary gorge, San Antonio Canyon
Hemming and Hawing on the Hogback: The San Gabriel Mountains are the steepest mountains in the world. Often the only flat spots are on dangerous stream floodplains and on top of landslides. Several examples from San Antonio Canyon include the Hogback and Cow Canyon Saddle
A Canyon as Deep as the Grand, and a Road For No Reason: The Glendora Ridge Road offers some of the greatest panoramas of any road in southern California, and there doesn't seem to be a reason for it being there. I suspect I know what the reason is
The Forbidden Valley: An introduction to the San Dimas Experimental Forest
A Minor Challenge: A quiz to introduce the unusual geology of the Santa Clarita Valley
Dreams of Avarice and the First Gold Rush: You thought the gold rush started in the Sierra Mother Lode? There was a rush six years earlier, but the Mexican miners kept their secrets better (and there wasn't very much gold, either)
The Oldest Rocks (Well, maybe...): The San Gabriel Mountains have very old rocks, maybe the oldest in the state. But it depends on how you define "oldest". A short introduction to radiometric (isotopic) age dating



PENINSULAR RANGES
A granitic mountain block vaguely similar to the Sierra Nevada, but also very different. The "peninsula" refers to Baja California, which makes up the bulk of the province

The Other California: Another Friday Fun Foto: A brief introduction to San Jacinto Peak, the highest mountain in the Peninsular Ranges, and one of the most prominent mountains in the state, with a 10,000 foot slope in one area.
A Mystery Photo for the Day: A view of a rock that looks like it belongs somewhere in the Sierra Nevada, but that is not where it is...
When is a Peninsular Range Not a Peninsula? Baja California is a peninsula, but the rocks continue into Alta California. This post explores the village of Idylwild next to the highest part of the province at San Jacinto Peak.
The Deepest Pass in North America, and Finally Taking THE Tramway: Well, sure, the Palm Springs Aerial Tramway is on a lot of postcards, but how many of them tell you the geological story?


I clearly have lots of ground to cover, and will update this page as necessary.

Thursday, July 8, 2021

My Thesis Area is Misbehaving: 6.0 Earthquake Near Walker, California

 

That was exciting. I live in the Central Valley of California. The valley is famously boring for a number of reasons, and one of the good ones is because we rarely feel earthquakes here. But that wasn't the case today. I was at my computer station and the desk started vibrating and I had to look and see if my wife was shaking it. She wasn't and she was not looking happy. 

It took a while for the USGS to untangle the many wave signatures in the seismic network (there was a brief report of a 4.8 quake just 20 miles from us), but as things have settled out, it looks like the quake took place smack dab in the middle of my masters thesis area in the eastern Sierra Nevada at the small town of Walker, California. The most recent estimate of the magnitude is 5.9 (upgraded to 6.0). The quake has the signature of a normal fault, the kind of faulting to be expected in a crustal region that is being stretched apart. 


Walker is the village in the picture above at the south end of the Antelope Valley, which exists because of faulting. The valley has sunk as the mountains on the right side of the photograph rose along the fault indicated by the solid black line. The epicenter of the quake would be just out of the picture on the lower right side (the picture is looking south).

Antelope Valley sits astride the boundary of the Sierra Nevada and Basin and Range provinces, where the solid block of the Sierra is being sliced up into a series of fault-bounded grabens. The picture below shows the upper (southern) end of the valley from Monitor Pass, with the Sweetwater Mountains in the distance. 

The next picture is from the hill behind Walker looking north. The break in slope on the left is where one would look for evidence of recent earthquakes, but slopewash has covered the fault terraces (scarps) in most places except for the streams and alluvial fans that cross the fault trace. That was what I was searching for when I was doing my masters thesis many years ago in this valley. I was very pleased when I found some.


The person who did the original mapping in the 1950's was working primarily on the rock exposures, and wasn't really looking for recently active faults. By the 1980's a number of people were looking a lot harder, trying to determine the seismic hazard for the region. Fresh alluvial fans provide a possibility of dating the occurrence and size of the last earthquake to cause ground rupture in an area.

The picture below is the Mill Creek fan, at the extreme south end of Antelope Valley. Under normal circumstances, an alluvial fan should be a smooth, gently sloping surface. Here at Mill Creek, the surface steps down to the left, forming a terrace. Immediately after the earthquake this terrace may have been essentially vertical (examples of scarps are shown on this post - Slinkard Valley lies immediately west of Antelope, and the post has a nice cut-away showing the arrangement of the fault blocks).

Scarps like these show that the last major earthquake took place in the recent geologic past, very likely less than 10,000 years ago, and maybe as recently as 3,000 years ago . The length of the fault and the size of the scarps are characteristic of quakes in the range of magnitude 6.5-7.0. A magnitude 5.8 event, the Double Springs Flat earthquake, shook the extreme north end of the Antelope Valley fault system in 1994. Today's quake one-upped that event, but do not be surprised if the magnitude is revised upward or downward (NOTE: the quake was revised upward to 6.0). It takes awhile to fully analyze the seismometer records. It is not inconceivable that some small cracks may appear along some of these older scarps.

I'm listening to reports of a rockfall off the cliffs above Meadowcliff Lodge. That would be very close to the epicenter.

I will revise this post as more information comes in. 

Postscript: I finally got to my office at Modesto Junior College to download the seismogram of the quake, and here it is. The shaking was off-scale for nearly two minutes.


The second shows a compressed version of the quake, along with some of the larger aftershocks.