San Gabriel Mountains National Monument Established Today! A Wonderful Moment

Looking west from Cow Canyon Saddle into San Gabriel Canyon, the heart of the new monument.

This is a big day for me, in the personal sense. The mountains I explored in my youth, the mountains where I learned to love the outdoors, are today being declared a National Monument. The San Gabriel Mountains National Monument designation is a long overdue recognition that the Los Angeles basin is surrounded by an extraordinary series of mountain ranges with unique and stunning geology, inspiring scenery, and unexpectedly pristine wilderness. For far too many years, the mountains have been abused, by both vandals and arsonists, but also by bureaucrats who never quite recognized the treasure they neglected.

I will have much to say in coming posts about the incredible geology that is part of the story of the San Gabriel Mountains. For now I simply want to say congratulations to those who labored long and hard for this day to happen. And thank you to President Obama for recognizing the value of these precious mountains.

The Other California: Adding Context to a Friday Mystery Photo

I am always pleasantly surprised by the insight of the commenters on this blog, especially in light of yesterday's mystery photo. I provided very little in the way of clues, but many of you saw things that I didn't when I was standing on the hill above the outcrop. Part of the difficulty was that I was on the top of the hill without binoculars, and the photo (taken by Mrs. Geotripper) was on an extreme zoom. I was also flying blind, so to speak, with no maps or field guides about the road we were on. So today I am providing lots of context to judge what's going on in the picture. This will be a two-parter...

First is the google image of the site (above), and a wider view of the outcrop (below). One thing that stands out about the San Gabriel Mountains is the extreme steepness of the terrain.  As I have noted several times (here, for instance), the only flat places are on river floodplains or the tops of landslides. That makes the green thicket of trees on the upper left of the GoogleEarth image immediately interesting. Why are the trees there, but not in other parts of the canyon floor? The second thing to note is the constriction in the canyon on the downstream side of the floodplain forest. Why is it there?

The third feature is the linear nature of the canyon itself. Streams tend to erode sinuous gorges unless the underlying geology (i.e., weak, easily eroded rock) is guiding the direction of the river carving. Why is that canyon so straight?

Here is the context shot. The dark oak tree in the upper left can be seen in the GoogleEarth image in the lower center as a dark dot where the canyon widens just downstream of the forest. The "outcrop" lies in the midst of the wider floodplain at the very bottom of the satellite image.

The linear canyon is rather adequately explained by the presence of a fault juxtaposing two kinds of rock. The rock on the west side (below) is an Oligocene terrestrial conglomerate-sandstone called the Vasquez Formation (known also as the Sespe Formation).

The gray rock on the east side (right side in the GoogleEarth image) of the fault is the Pelona Schist, a rock composed of parallel layers of muscovite mica and quartz grains. The rock is not overly tough, as the mica is soft and the layers separate easily. The Pelona is subject to landsliding...

Here is a final context shot for the mystery (below). The story is perhaps becoming clearer: the San Gabriel Mountains have been rapidly uplifted, so that even weak rocks have been deeply eroded and formed steep slopes. Fault lines cross the mountains, including this locality, so the canyon eroded in a straight line that divided the Vasquez Formation from the Pelona Schist. The Pelona is prone to slope failure, so ancient landslides blocked the stream, forming temporary lakes that filled with sediment, providing a nice environment for the growth of a riparian forest. The constriction in the canyon is the site of the old landslide.

All of which doesn't exactly provide an answer to yesterday's mystery. Many commenters (who never cease to amaze me with their insight) suggested the idea of a debris flow, and this is correct in a way. Others noted the regular pattern of holes and suggested that the outcrop has been quarried or otherwise altered by people. Also true, in a way.

Before I stumbled onto what was going on, I was thinking that this was an outcrop of the Vasquez conglomerate, but I was bothered by the bleached aspect (the Vasquez is red-brown). I thought maybe I was looking at a displaced fault sliver in which hot acidic groundwater had altered the original material. But when I saw the holes much later while processing the digital images, I realized I was looking at something much different. And something very tragic...

The next post may be titled "They didn't. Surely they didn't put it there..."

The Other California: A Canyon as Deep as the Grand, and a Road for no Reason

OK, not quite as deep as the Grand, but who's to quibble over a few hundred feet? That's what I love about California: it has a lot of famous places that everyone has heard about, places like Yosemite, Death Valley, and Big Sur, but it also has many corners that are known locally perhaps, but are not all that prominent in the public consciousness. They are parts of state parks or national forests, sometimes private lands, and they offer geologic treasures that would be national landmarks in any other setting. That is the theme of my sporadic posts on the Other California, a description of these unheralded places.

The beautiful skyline in the photo above comes from the high point on the Glendora Ridge Road, a paved highway with no picnic areas, no campgrounds, no signed overlooks, and no particular destination or purpose that is obvious. The road connects Baldy Village at the east end of the San Gabriel Mountains with roads rising out of the San Gabriel River and the urban sprawl of the Los Angeles Basin around Glendora and San Dimas.
For such an unpublicized road, the Glendora Ridge Road is spectacular. It winds across the top of a high ridge, a fault block caught between the now inactive San Gabriel fault and the highly active Sierra Madre-Cucamonga fault system along the steep mountain front. The rocks include beautiful exposures of Proterozoic gneiss and schist, some of the oldest rocks in California, along with Mesozoic or early Cenozoic granitic rocks (some gneiss is shown in the photo at the end of this post). To the north, the road provides a bird's-eye view of one of Southern California's more dramatic wild areas, the Sheep Mountain Wilderness. It always seemed inconceivable to me that such a place could exist just 10 miles as the crow flies from the urban sprawl of the Los Angeles basin. The wilderness encompasses nearly 8,000 feet of vertical relief from the bottom of the East Fork of the San Gabriel River to the summit of Mt. San Antonio (Mt. Baldy). The canyons are immense, with depths exceeding 4,000 feet in a few places. The rivers (another SoCal rarity) are so rugged that few trails reach them, and at least one of them is a natural trout fishery (Upper Fish Fork). The wilderness is an ideal habitat for the rare Nelson's Bighorn Sheep. I was lucky one year while hiking on the boundary of the wilderness; I chanced upon a herd of a dozen or more. Being who I am, I fumbled in my pack for a camera (one of the old-fashioned kind with this stuff inside called 'film'). They heard the noise and skittered away. I got a great picture of a dust cloud...

Mount San Antonio (10,064 feet) is the highest point in the wilderness. The summit is hidden by clouds in the pictures below, but the mountain is one of the most familiar sights on the Southern California skyline. Thousands of people hike to the summit every year along a trail that starts at the Mt. Baldy ski area. There are two other approaches to the summit, but the number of hikers every year on those routes probably numbers in the dozens. A long and rugged trail approaches from the north part of the wilderness over Dawson Peak and Pine Mountain. Perhaps one of these days my brother will guest-blog about the time we, uh, "misplaced" him on this trail during an Explorer Scout backpack trip...


The other trail to the summit starts at Baldy Village and climbs almost 6,000 feet to the summit. To call this a difficult trail is nearly an understatement, but climbing it was one of the great adventures of my youthful days. Hot and dusty in the lower reaches, and spectacular views the whole way up. It's a good place to catch sight of the bighorn sheep.

There is no official Sheep Peak, by the way. It is the informal name of the prominent peak in the center of the wilderness area, 8,007 foot Iron Mountain (the prominent peak on the right in the picture below). I've never had the privilege, but the climb to the summit is said to be one of the toughest hikes in the south state, with great views and a chance to explore some old gold mines along the way.
Glendora Ridge is paved and well-maintained. That it exists is kind of a mystery to me, and I welcome any explanations as to why it was built. According to Russ Leadabrand (a travel author and Sunset Magazine contributor in the 1960s and 70s), the road was constructed in the early 1930s. I have thought of one possible reason. After my comments a few weeks back about the hazards of living in Southern California, especially adjacent to the high mountain ridges, it occurs to me that Baldy Village would have but a single access road if Glendora Ridge Road wasn't there. A single way out in the event of a major earthquake, a major flood, a major fire, or big landslide. The same problem applies to the developments in San Gabriel Canyon off to the west, a highway that also connects with Glendora Ridge. It looks to me like Glendora Ridge Road is the evacuation route... Whether it is or is not the escape route, it is a great road to drive. Unfortunately the local kids with their newly minted driver licenses know about it too, and a Google search on the subject of the road is likely to turn up stories of tragic car crashes as much as anything else (one of my high school buddies survived a 400 foot plunge off the highway). But for us last month it was uncrowded, and with the clear December skies, a beautiful excursion looking towards the high mountains, and the crowded valleys below.

There are some great rocks exposed along the highway...

The Other California: Hemming and Hawing on the Hogback

The nearly unprecedented deluge in California, Nevada, Arizona and Utah reminds me that I need to finish up some old business. Piling up a foot or more of rain on slopes that were burned in the last few years is a dangerous situation that can lead to mudflows and other slope failures problems on the steep slopes surrounding the L.A. Basin and California's Inland Empire. But such events have long been part of the history of the mountains, dating to long before humans entered the picture.

On Friday I posted a question about the Hogback in San Antonio Canyon in the Transverse Ranges of Southern California: what is it? It was an imposing barrier to my little VW Bug when I drove up the canyon decades ago, and it looks out of place, but it fits in very well with the dominant geological processes in the steepest of mountain ranges, the San Gabriel Mountains. That process is mass wasting, the failure of slopes and rock masses under the influence of gravity. Rock falls, debris avalanches, slumps, earthflows and soil creep are all common forms of mass wasting.

A view of the hogback from upstream (this shot is from Cow Canyon Saddle) gives a better view of what happened. A large mass of rock slid from the slope on the right, breaking up as it covered the canyon floor. It dammed San Antonio Creek, forming a temporary lake. Within a few centuries the lake filled with rock and debris, forming one of the few flat areas in the canyon, which much later allowed for a small village to be developed on the canyon floor. Ironically, many of the developments in the San Gabriels are built on mass wasting deposits (Wrightwood is built on mudflow debris and is sited atop the San Andreas fault for good measure, and Crystal Lake is an avalanche deposit as well).

The rock slide is nicely exposed along the old highway, with a clear delineation between the lighter colored slide breccia on the left and brownish river gravels on the right. In retrospect, placing a highway at the toe of a huge rock slide next to a volatile stream seemed a less than bright idea. As noted before, the current highway goes over the top of the slide.

San Antonio Creek was forced into the left wall of the canyon (from the upstream side), and it started to carve directly through the solid bedrock, forming a deep gorge with a 30 foot waterfall. The sheer cliffs below the waterfall are used as a practice wall by technical rock climbers.

Once you know what to look for, many instances of mass wasting become obvious throughout the canyon. The rock mass above lies near the entrance of Icehouse Canyon, and drivers must climb a series of steep switchbacks to reach Manker Flats and the ski area in the canyon above. Another rock mass, at Cow Canyon Saddle, tells a very interesting story about the formation of San Antonio Canyon (below).

The upper part of San Antonio Canyon abruptly changes direction near Baldy Village, and Cow Canyon Saddle is situated at the turn. To the west, Cow Canyon drains into the larger and deeper San Gabriel River system. Before the landslide took place, upper San Antonio Canyon probably drained to the west into the San Gabriel River. The slide at Cow Canyon Saddle blocked the ancestral canyon, and diverted the drainage into the lower San Antonio gorge (or headward erosion quickly captured the dammed up drainage).

It will be interesting to see if any major changes took place in the canyon after the events of this week...

The Other California: The Mountains of My Youth

I grew up under the east end of the San Gabriel Mountains, a huge terrane of Proterozoic and Paleozoic metamorphic rocks intruded by Mesozoic granitic rocks, and squeezed up like a watermelon seed between the San Andreas fault and the Sierra Madre-Cucamonga fault system. I have heard that the San Gabriels have the statistically highest average slope of any mountain range in the world, and having hiked and climbed these mountains in my youth, I find the statement plausible.

As with many things of youth, I kind of took the mountains for granted, thinking the far away Sierra Nevada as the "real" mountains. The Sierras were only accessible during summer vacation, so the San Gabriels served as a mere substitute camping and hiking locale while waiting for school to get out. Having made a few excursions into the region recently after a thirty year absence, I am reassessing that opinion. The San Gabriel Mountains are a rare treasure. How many of the millions of people in the Los Angeles Basin-Inland Empire region are aware that they have gorges that are nearly as deep as the Grand Canyon in their backyard? Or that the pebbles in their alluvial fan backyards are some of the oldest rocks in the state, at nearly 2 billion years? Or on a more menacing note, that those pebbles arrived in their backyards via numerous monstrous mudflow events? Actually, I think some people are aware of that last one, especially in light of some of the recent wildfire disasters in the region.

Today's first picture is of Cucamonga Peak, which rises to 8,859 ft (2,700 m) from the apex of the alluvial fans at the mountain base at about 2,000 feet. That's a gain of about 7,000 in a horizontal distance of three or four miles. These are steep and high mountains! The canyons that carve the deep gorges on the flanks of these mountains are dangerous environments in the long run. Mass wasting in the form of rockfalls, debris avalanches and slumps accomplishes much of the erosion, and the intermittent streams that run through these valley are prone to disastrous mudflows.

San Antonio Canyon is one of the steep canyons that is well known to locals, but not so much to those outside the region. It drains the slopes of Mt. San Antonio (10,064 feet) and a ring of 8,000 and 9,000 peaks tucked behind Cucamonga Peak in the photo above. A paved highway provides access to tiny Mt. Baldy village and a modest ski resort (did you even know that southern California has skiing?).

The lower canyon can be described quite accurately as ravaged by both nature and man, as the region is regularly swept by wildfires (natural and not). The 'floodplain' is choked with debris from numerous mudflows, and few trees can gain a roothold on the valley floor. The slopes above are almost impossibly steep.

The roadmakers tried to maintain the highway on the valley floor, but the picture above shows how that worked out. The highway today winds along slopes hundreds of feet above the creek. In the upper canyon, the high peaks are dramatically revealed, and conifers make an appearance, mostly Bigcone Spruce, Jeffery Pine, and Incense Cedar.

VW Bugs (1960s vintage) were wonderful cars, but my poor car had to drop into first gear to surmount the biggest obstacle in the canyon, the Hogback. It is just above and left of center in the picture below. Mt. Baldy Village is tucked into the area just beyond, and the major trailheads come a bit farther up the road.

For my fellow high school students, the Hogback was a test of one's manhood (and it was mostly guys). They would take their muscle cars up and down the highway at speeds approaching 90 mph, and some would make it out of the canyon. Others didn't. One morning a friend showed up at school sheepishly bearing bandages and scratches. A bit of questioning revealed that he had missed a curve and ended up 400 feet down the slope on the canyon bottom. I almost died at the top of the Hogback; I was driving my family up the road with my newly issued drivers permit when someone came down the highway passing on a blind curve and running us off the road.

As a pre-geologist in the early 1970s, I thought the Hogback was out of place and out of character with the canyon. I have come to realize that it is very much in character with the canyon, so I leave you with this question: What is the Hogback?

I should probably invoke some sort of Schott Rule on those geologists that live in the nearby towns, but I won't, so answer away!

The Other California is my continuing series highlighting the geology of the fascinating places in my fair state that don't often show up on the postcards that tourists buy. The state is a big place and I have yet to see it all, so if you have a favorite corner of the state and would like to put together a blog entry, I would gladly add it to the series.

It was a day like no other...and that's the problem

A thousand real estate agents abandoned the shopping malls, grabbed their cameras, and snapped pictures today in southern California. Why? Because it was a gorgeous clear day like no other...and that's the problem. If you sell property in SoCal, your pictures of houses for sale have big beautiful mountains in the background. Mountains that are commonly invisible when you actually live there. Given the all-too-common state of the air in the basin, this could be called false advertising.

In the first years of my youth, I lived in the Inland Empire, the citrus-growing region around Riverside, Upland and San Bernardino. There were smog problems back then, but most people accepted that as a fact of life, the cost of living in big cities. The ring of mountains surrounding our valley guaranteed that the poisoned air could not escape and be dispersed across the desert. In those days of the 1960's, no one could conceive that anything could be done about air pollution, much less that it should be. I grew up next to a steel refinery which, their media officials proudly pronounced, produced only 15% of all the smog in southern California. But dammit, they employed thousands, and even offered medical benefits (ever wonder where Kaiser Permanante came from?). Air pollution was the symbol of a booming economy, even if it was sickening and killing the people who had to live in it.

I have memories of the vast wall of yellow gunk streaming over the Chino Hills most afternoons, and after a time a smog alert would be issued and p.e. class would be canceled that day. It would physically hurt to take a deep breath. That was just the way things were, and there wasn't anything that could be done about it. There is still plenty of pollution, but for the actions we chose to take the Los Angeles basin and the Inland Empire would have ended up looking like the L.A. of the movie "Blade Runner".

The Clean Air Act made a difference. Even though the population has perhaps quadrupled since I lived there, pollution systems in cars and factories have improved air quality to a huge degree. It would never have happened without government intervention, and we are all the better for it. I think of the Clean Air Act and other landmark legislation that made life better for all of our population, not just a chosen few. Politics has always been about getting the advantage for those stand to make the most money, but once in a while we can force politicians to rise above their base instincts and really do something for the good of the country.

The ranges in these pictures are the mountains of my youth. I have stood on many of these summits, and explored many of the canyons hidden in the folds of the jagged rock. The first picture shows the rugged eastern end of the San Gabriel Mountains, the high ridges of Cucamonga Peak, Ontario Peak and Mt. San Antonio, ranging from 8,000 to 10,000 feet in elevation. They are composed of plutonic and metamorphic rocks ranging in age from Proterozoic to Mesozoic time. The mountains have risen rapidly in the last few million years, and have been described to me as statistically the steepest mountains on the planet. Indeed, the only places flat enough for developments in these mountains are on landslide deposits (Baldy Village and Crystal Lake, for instance). The town of Wrightwood, besides being sited on top of the San Andreas fault is also occasionally damaged by mudflows from the unstable slopes above.

The high ridges in the second picture are in the San Bernardino Mountains, the highest mountains in southern California. They are also composed of plutonic rocks, but also include Paleozoic metasedimentary rocks with affinities to those in the Mojave Desert. They are quite unlike the adjacent San Gabriel Mountains, which is hardly a surprise given that the San Andreas fault passes between them. The rocks of the San Gabriels originated far to the south, and have been carried north by lateral motion along the fault. The high ridges of San Bernardino Peak made an ideal location for the initial survey station for the township and range system of property boundaries across southern California. The primary east-west survey line is called a "baseline", and if you stand in the middle of Baseline Avenue as it runs through Claremont and Upland, you will see that it lines up exactly with San Bernardino Peak in the distance (you need a clear day, and watch out for traffic!).

I am trying trying to build a photographic record of some of the places I grew up in as part of my "Other California" series, so look for a few entries as I revisit the mountains of my youth. In the meantime, I recommend a wonderful book published by Stephens Press called "Call of the Mountains" by Ann and Farley Olander. It's a wonderful photo essay of the San Gabriels, the San Bernardinos, and the San Jacinto Mountains, the not-quite-fully appreciated jewels of the mountains of Southern California.