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Facets of the Natural World around Us ....
June 20th, 2009
The sound of a muffled shriek, coming from the seat behind, made me look ahead.
I corrected the vehicle’s path instantly, putting it back between the yellow lines, so to speak. Fortunately, we had been going only about five miles an hour. What had happened? Well, it was a quick but typical instance of geologist’s “Road-Cut Attention Deficit Disorder”.
RCADD is little known among the general population, but well known among geologists.
It is the tendency to be distracted by the rocks in a road-cut or on nearby cliffs, let’s say, while driving past them. (What are those rocks? Where did they come from? What does their structure mean?)
It is not the kind of thing you want to have kick in while you are speeding along the edge of a precipice, or on a busy freeway — especially if the geologist is the driver, and you are the passenger.
In this case, I had been driving some tourists from out-of-town down one of the pretty little residential roads high up on the south side of Camelback Mountain.
We had been looking at marvelous views of the valley, peering through people’s back yards and over rooftops, at South Mountain in the distance, the Sierra Estrella, and the groves of downtown skyscrapers sprouting out of the layer of brown murk that was no doubt at that very moment causing the eyes of the down-towners to itch and burn.
We had rounded a bend, and that is where I saw it. There, just behind a Palo Verde tree, at eye level and only about 15 feet away, was a giant boulder of very old granite about three feet across, rounded along most of its edges, suspended in the midst of the red sandstone that make up the cliffs that tower above the glamorous homes of the neighborhood we had been invading. That was when RCADD had hit me.
To the non-geologists next to me, and in the back seat, the puzzle hadn’t registered. After I had adjusted our trajectory, and everyone had breathed a sigh of relief, I explained why I had become so distracted.
Here was a classic geologic anomaly. How is it, that this big rock could have been deposited right down into the depth of the fine sand? Think about it. Sand like this is usually laid down by relatively slow moving water, or maybe even wind, as in sand dunes.
How did the heavy boulder get carried into this setting, and just dropped off, before being buried by even more sand? And keep in mind that whatever happened here happened about 25 million years ago — it’s not just evidence of an accident yesterday by one of the construction crews finishing off someone’s million-dollar back patio!
That one boulder is to me the most curious example of a type of strange geology you can see in several places around Phoenix. The west end of Camelback Mountain, and the buttes in Papago Park are the best places to see these rocks whose formation stretches my imagination, as well as that of other geologists.
One current theory ascribes their genesis to “long runout landslides”, also known as “sturzstroms”. Maybe in an instant, on a nice summer morning much like today, by a process not yet well understood, a monstrous amount of sand and rock collapsed from the steep slopes of mountains that stood just east of the present- day metro area.
A vast mixture of rock, sand, and debris rolled out over the flats, at first glance possibly looking much like one of the big dust storms we see during the monsoon season here in Phoenix, but devastating beyond comprehension.
The landslide flowed for many miles, basically along a layer of air, and then it just stopped dead in its tracks. The theorized mechanism behind such a phenomenon is given the name “acoustic fluidization”.
Hard to believe? Yes. I kind of want to see one before I can really buy into this theory. There are some modern-day cases of smaller events, however, that seem similar. One happened during the large 1959 earthquake near West Yellowstone, Montana.
There, at a place just below Hebgen Lake, a mountainside collapsed, flowed instantly down and across the small valley, even running part-way up another mountain on the other side of the river. That landslide obliterated a campground, at once killing 28 people, who in their sleep never knew what hit them.
You can see some such unusual rocks just by looking out the window as you drive along McDowell Road between the Papago Buttes. You will see large (and small) chunks of granite caught up in reddish sandstone, like dried-out, jagged bleached plums in rusty, desiccated pudding.
If you spend more than a few seconds looking, watch out! You, too, have RCADD.
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Tags: Camelback Mountain, Earth & Evolution, psychoGeology, Valley of the Sun
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May 14th, 2009
Let’s talk about gold. Not just any gold, but lost gold. If there’s one thing more appealing than found gold, it’s lost gold. Because that means that the gold – maybe an unknown, vast quantity of it – is still out there somewhere, just waiting to be found. Like fairy-dust sprinkled from a magic wand to vitalize some situation, a dusting of the lure of gold can make a place attract people – those people looking to make it big.
Sometimes they win; sometimes they lose.
And sometimes they die.
We have our own place of temptation right here in our backyard: the Superstition Mountains. For the past century or more, this rugged range of desolate, inhospitable, and yet beautiful rock formations just to the east of Phoenix has drawn countless treasure seekers. The goal? A mysterious cache of gold, or gold ore, or maybe even a mine itself. Who knows which? That’s part of the mystery, and the draw of the place.
In 1891, one Jacob Waltz, a German immigrant and prospector, known locally as the “Dutchman” (men from both the Netherlands and Germany were then frequently called that in America), died in the Phoenix home of a friend, Julia Thomas. On his deathbed, Waltz described to her the location of a gold deposit of which he knew, deep in the Superstition Mountains. But in his possession then were only a few gold nuggets, and he never had appeared to be a wealthy man.
Yet, Ms. Thomas and two of her friends, the Petrasch brothers, believed that there was something to his story, and they set out to find it. They spent weeks roaming the wilderness, searching for whatever they could find, which ended up being nothing. Julia Thomas did find a way to capitalize on the Dutchman’s fate, however. She drew up and sold some “treasure maps”, as well as told Waltz’s story to at least one freelance writer, who in turn embellished it even further.
Hence, the story grew, and multiplied. And so today, there are almost too many “Lost Dutchman” stories of which to keep track. (And remember, it is the gold that was lost, not the Dutchman.)
There are variations which include Mexican miners (who supposedly originally found the gold), Apache Indian raiders (who killed the Mexicans and maybe even Waltz’s sometime mining partner, Jacob Wiser), high-graded gold ore stolen by Waltz himself from near Wickenburg and stashed in the Superstitions, and even Jacob Waltz having murdered his partner to hoard the gold for himself.
The wildness of the terrain, the relentless, blazing sun and lack of shade, the dearth of water in the remote desert canyons of the Superstitions, and a colorful cast of crazies, desperadoes, and dream-seekers who have over the years spent countless time seeking out the rumored riches have only added to the luster of the story.
The details of all these legends and maps do not matter so much as the fact that they exist, and that the story of the lost gold endures – the fascination goes on. Over the years more than two dozen adventurers have lost their lives, in one way or another, while exploring the range.
The derivation of the name “Superstition” is not even certain. One version is that in the 1500’s, the Spanish explorer Francisco Vasquez de Coronado apparently gave the mountains that name, based on the Apaches’ claim that therein lay the abode of spirits, ones who did not look kindly upon intrusion, especially in the name of profit.
Only a few years after Jacob Waltz’s passing, hard-rock gold was discovered not far from the north side of the range, near what is now the little mining town of Goldfield. Millions of dollars were taken from the ground during the heyday of mining operations there.
That a true in-situ gold deposit does exist in the Superstitions themselves is very unlikely. As I’ve mentioned in several other GeoStories™ (“Tuff Times”, and “One Piece at a Time”), the range (in this case, the western end, of which is to where the legends refer) is built-up of thousands of feet of ancient volcanic ash, fused into thick, resistant layers which today have eroded into a maze of pinnacles, ridges, and gorges. Barren volcanic cinders – now rock – and that’s all. Barren of precious gold, that is, but not of dreams.
Take a look at the Superstition Mountains from a distance, in the setting sun sometime. If you give pause for a moment, they look yellow, even golden. It’s that would-be coating of gold dust out there that you see.
That and the glimmer in your eyes.
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Tags: Gold, psychoGeology, Superstition Mountains, Valley of the Sun
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April 21st, 2009
Arizona has a violent past, and by that I’m not referring to its “wild west” days. I’m talking about its “rocky” history, so to speak. And as you and my other loyal readers know by now, it’s the rocks, quiet now though they may be, that reveal glimpses of distant antiquity and times when the world here was a very different place.
In many places around the Valley of the Sun lie smooth, gentle-looking rocks that belie their origin. They weather into rounded slopes and rivulets, and many various-colored lichens love living on them. They even look like badlands in places, only on a miniature scale, and the surreal shapes they exhibit could give even Salvador Dali a lesson or two.
You can see them in the Superstition Mountains, the Goldfield Mountains, and out west of us in the Hieroglyphic Mountains, near Lake Pleasant. Some of the more scenic arrangements show golden or ocher colors, forming layers within other craggy, forbidding-looking rocks.
Many people are surprised to learn that these picturesque rocks are simply volcanic ash – dust and cinders that fell from the sky after our landscape in other times was shaken and blasted by massive volcanic eruptions – really gigantic eruptions.
If you had been living in this area sometime between about 25 million years ago and around 15 million years ago, you would have had a chance to see one of a series of absolutely amazing sights: an eruption of a volcanic caldera. It would also have been the last thing you ever witnessed. It’s hard to say whether you would have been vaporized first, and then completely blown-away, or if it would have happened the other way around.
Where the Superstition Mountains now sit, evidence remains of at least three of the major eruptions, each resulting in a caldera formation. A volcanic caldera is like a crater, without a tall mountain cone surrounding it.
Calderas are also very big – the ones of the Superstition Complex are 10 to 15 miles (16 – 25 km) across, each. They form when molten rock, called magma, suddenly and explosively belches from the Earth’s subsurface, where it has been slowly, relentlessly, pooling and heating in great volume.
Some kinds of molten rock merely flow when loosed onto the landscape, but the kind that spews forth from calderas is thick and viscous, and when it reaches the surface, it blasts out and expands with awesome force.
The resulting devastation can reach out thousands of miles (or kilometers). Several decades ago, in Washington State, we witnessed the spectacular and deadly eruption of Mt. St. Helens. That eruption of magma was of this type – explosive. But that peak was, and is, no caldera. It is only a volcano, and its crater is less than a mile (1.6 km) across.
Even so, ash from that event fell hundreds of miles (or kilometers) to the east. A few hundred miles (or kilometers) south of St. Helens lies Crater Lake, Oregon. There you can see an old caldera, although a small one. It is now filled in by a shimmering lake of sapphire color, and that scenic, circular opening is what is left of a mountain that blew its top some 8,000 years ago, and its subsequent collapse into the void below.
The Superstition Mountains, and, to a large degree, parts of the other above-mentioned ranges, are composed of thick layers of volcanic ash. In some places, you can readily see the layers.
For the most part, the ash layers are now very hard rock, for when it fell from the sky, the ash was white hot, and the particles all fused together when they settled down.
Some ash was cooler when it fell, so it fused to a lesser degree, and those layers are now more crumbly and easily eroded.
One such thick layer (hundreds of feet, or meters) is known as the Geronimo Head Formation, and it is easily recognizable as a yellowish band, which has smooth, curved surfaces, and usually lots of those splotchy lichen colonies that thrive so well there.
This kind of rock is called a tuff in “geology-speak”. And because it is mostly silica, like sand, it is fairly devoid of other minerals. So, Lost Dutchman’s Gold fans, your chances of yellow metallic treasure being in there somewhere are pretty slim.
Are there any such calderas active in the world today? The answer is yes. One is now called the Yellowstone Caldera, in Yellowstone National Park. The last time it erupted was about 600,000 years ago – a mere blink of an eye ago, geologically speaking.
When it bursts forth again – and it surely will – those people nearby and downwind of it had better have their disaster plans and supplies ready and waiting, those people being the residents of Montana, Wyoming, Idaho, Alberta, Saskatchewan, North Dakota, South Dakota, Iowa, Minnesota, and ….
Oh well, you get the idea.
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Tags: Earth & Evolution, Superstition Mountains, Valley of the Sun
Posted in DBG Hikes, General | No Comments »
March 27th, 2009
“Sandstone. It’s sandstone, I think.”
Those words came loudly from behind, as I was standing in the warm, late-day glare, taking in the sweeping panorama in front of me. I quickly turned around to see two lady hikers talking to what looked like a group of students from a nearby high school, out for an afternoon workout or field trip. I reasoned that maybe it was a physical education class. I hoped it wasn’t a science class, because whichever had answered someone’s question was wrong.
The pair appeared to be teachers, and they were just getting their youthful group started back down the trail from the summit. Like me, they had all been spending a few moments, transfixed, at the top of the hill, since the vista of Phoenix from that spot was really quite good, and there was even a slight, cooling breeze.
In the distance to the southeast, I could clearly make out the tall buildings of downtown. To the west, I could see the city all the way out to the White Tank Mountains, and right below me was a whole series of small winding lakes, each one tightly surrounded by upscale homes.
I knew I couldn’t let the error go. I just had to do some correcting, and besides that, I’m not one to turn down a chance to talk to some pretty ladies.
“No, it’s basalt,” I yelled to the them, then about thirty feet away.
The blonde one looked over at me, the expression on her face saying, “so who are you?”
I explained, “I thought I just heard one of you say that the rock we are standing on, and all along this trail, is sandstone, and it’s not. It is a rock called basalt – it’s volcanic. I know, because I am a geologist. Look at the frozen bubbles in it.”
“Oh,” she said humbly, surprised at my interjection. She must have been the one who had made the sandstone statement. “Thank you.” And with that they headed down the mountainside, eager to catch up with some of the kids who had already gone on ahead. Apparently they had not been as anxious to talk to me as I had been to them.
But, hey, I don’t blame them. You never know what kind of weirdo you might meet out on the trail. You might even meet a geologist – one just itching to explain the rocks to anyone who will listen.
Now, don’t get me wrong. I don’t make a habit of hanging out along local trails, waiting for unsuspecting hikers to come by, just so that I can leap out and impress them with geological knowledge. But neither can I stand by and let a misconception go uncorrected.
There is a reason we could call these peaks Phoenix’s “black hills”. This interlude took place on one of the high points of the Hedgpeth Hills, a group of rounded, small mountains that lie mostly along the north side of SR 101, the Agua Fria Freeway. Much of the range here looks rugged, forbidding, and black.
Actually, however, thanks to the City of Glendale Parks and Recreation Department, there are several nice trails within this refuge. Known as Thunderbird Park, it presents several magnificent viewpoints from which to gaze out over our vast valley. Named in the past after Robert Hedgpeth, a early homesteader in the valley, the hills were then just lonely hulks out in the middle of nowhere.
On that particular day that I was giving the free, unsolicited geology lesson, the rocks had greater contrast than usual. It was because of the absolute profusion of brilliant, yellow Brittlebush plants that literally carpeted patches of the hillsides. The moist smell of springtime filled the air, and just walking through thickets of that golden brush left smears of bright yellow pollen on my clothes.
As I walked back down the path, well behind the class, I hoped there were none of those sociable little killer bees around waiting to massacre me on that rocky hillside. Basalt covers much of the Hedgpeth Hills.
As I have written before, basalt is an igneous rock (igneous means “from fire”) that flows easily and readily when molten. It is heavy, and when hardened it eventually erodes and forms dark rubble on the desert slopes that sort of looks like a multitude of coal-colored avalanches.
Among the youngest rock in the Phoenix area, here it is approximately 15 million years old. There are different, older rocks at the west end of the Hedgpeth Hills, but to me, they are not as striking, or as moody-looking, as the basalt is.
Basalt also makes for a good rock on which to inscribe petroglyphs. At the eastern end of these hills is the Deer Valley Rock Art Center, where there are well over a thousand ancient petroglyphs, some as old as 7000 years. You can get a good “feel” for the rocks there, also, and you don’t have to hike up a mountainside to do it.
And there are probably no geologists lurking in the background, either.
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Tags: Archaeology, Valley of the Sun
Posted in DBG Hikes, General | No Comments »
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