Fan of Columnar Jointing? Here's a Real Gem for You in the Sierra Nevada, and it's Not Devil's Postpile

Tucked away in a small corner of an unheralded canyon of the Sierra Nevada is a real gem of a geological locality. It is a marvelous example of columnar jointing that has been modified by glacial scouring, and it's NOT called Devil's Postpile. Welcome to the Columns of the Giants.

The Stanislaus River doesn't quite have the panache of the Merced River, which flows through Yosemite Valley, or the Tuolumne River, the architect of Hetch Hetchy Valley. It's not protected as a national park like Kings Canyon. It had glaciers during the ice ages, but they didn't have the volumes of ice necessary to carve stunningly deep gorges like the previously mentioned river valleys. But it does have a grandeur all its own.

The headwaters of the Stanislaus expose rocks that are quite distinct from those of the other more famous rivers. The rocks have a darker aspect, due to being composed of relatively young volcanic rocks, rather than the granite that makes up three-quarters of the Sierra Nevada. Highway 108 crosses one of the uppermost tributaries at Sonora Pass (9,624 feet/2,933 meters), and travelers can get a spectacular view of these former volcanoes that were active about 10 million years ago. They erupted onto a muted landscape of eroded granitic rocks. Some of the eruptions produced flows that traveled more than fifty miles downstream through the canyons of the Ancestral Stanislaus River. Later erosion acting on these flows produced the famous Stanislaus Table Mountain in the vicinity of the Gold Rush Towns of Jamestown and Sonora.

Beginning around 2 million years ago, glaciers began tearing away at the higher parts of the Sierra Nevada, removing many of the volcanic flows and carving U-shaped gorges like the one above, visible just a few miles downstream of Sonora Pass at Chipmunk Flat. The ice age was not a single event. The ice advanced and retreated more than a dozen times, with warmer periods in between that lasted for thousands of years. It was during one of these interglacial periods that something extraordinary happened in the upper reaches of the Stanislaus River drainage. Roughly 150,000 years ago there was a volcanic eruption down in the canyon.

It wasn't a large eruption, certainly not on the scale of some of the rhyolite cataclysms that devastated the regions east of the Sierra crest 767,000 years ago. It was more of a mild cinder cone eruption that might have flooded a portion of the canyon, flowing just a few miles downstream before the lava flows ceased. Subsequent glaciations scoured away much of the remaining lavas, and river erosion removed still more. Hidden in a cleft, a basalt dike just upstream of the columns may be all that remains of the volcano responsible for the eruption. It's not much, just the fracture in the granite that filled with basalt that fed the eruptions above. 

The remains of the lava flow, though? Spectacular! The lava flow (or flows; there were possibly two of them) was ponded by some obstruction downstream, most likely a glacial moraine, and a modest lava lake developed, several tens of meters deep. As the lava cooled, it shrank and the rock fractured in generally hexagonal columns roughly perpendicular to the surface against which the lava flowed. Since the lava flows were erupted onto a canyon bottom with slopes on either side, not all of the columns are vertical (this is also true of the better-known Devil's Postpile). 

Subsequent glaciations (primarily the Tahoe and Tioga stages for those who want to know) tore away at the lava flow, exposing the columns. Over the last 10,000 years or so since the last Tioga glaciers melted away, frost wedging has pried many of the columns loose, dumping them into a vast talus slope that covers the base of the lava flow. Cold air emanating from the base of the talus suggests that a mass of ice might actually remain deep within the rockpile. 

Columns of the Giants can be easily visited by following Highway 108 about 25 miles east of the Pinecrest Lake Resort area or 13 miles west of Sonora Pass. Overnight accommodations can be found at nearby Kennedy Meadows and a number of National Forest campgrounds. Educational groups may be able to make arrangements to stay the High Sierra Institute at Baker Station just a few miles away (contact the Yosemite Community College District for more information).

Stanislaus National Forest has provided a parking area and simple toilets for visitors, and a paved ADA-compliant trail and bridge provides access. The trail is only a few hundred yards long, and the visual rewards are great. 

Can't get there in person? My friend and colleague Ryan Hollister put together a marvelous virtual field exercise that provides an experience that is the next best thing to being there. It was featured on NPR's Science Friday a few years ago.

Anniversary of the Donnell Fire: Nothing in this World is Permanent, Except for Change

The Dardanelles Crest in 2006

On August 1, 2018, a fire started in the Stanislaus National Forest near Donnell Vista on Highway 108. It's not known how the fire started, but lightning was not the cause. It was clear that day. There wasn't much concern, it was confined at first to a few acres, but it blew out of control and started spreading. The so-called Donnell Fire ultimately burned 36,450 acres (57 sq. miles; 147.5 sq. km.) and destroyed 135 structures including the historic Dardanelles Resort. There were nine injuries, but thankfully nobody was killed.

The Dardanelles Crest, August 1, 2019

It was a coincidence, but exactly one year later to the day, we headed up Highway 108 to view the damage for the first time. It was sobering. The fire can't be compared to the devastating fires that ravaged Paradise and Redding last year or Sonoma County in 2017 when dozens of lives were lost and tens of thousands of homes burned. But still this fire was a tragedy. It burned memories and experiences. Like so many fires both in Southern California and in the Sierra Nevada, it took away landscapes that have shaped my life.

The Dardanelles in 2008

Fires have always been a player in the environment of California. A Mediterranean climate, with mild wet winters and long dry hot summers is an absolute guarantee that fires will burn. But we have entered into a new climate regime due to global warming that is deeply altering the patterns of fire in California and across the American West. Warmer average temperatures intensify the effects of droughts, causing greater evaporation and drier soils, so trees and shrubs are less able to deal with fires. The fires have increased in size to massive conflagrations, and burn more intensely, "crowning" more easily, and at times altering the soils so they are less able to absorb moisture when precipitation does come.

The Dardanelles on August 1, 2019

It was a relief to see that in many areas the fire took on a checkerboard aspect, missing some of the forest groves, which means that the forest can re-seed more readily. In other areas, the destruction was more complete, as in the slopes above the former Dardanelle Resort, seen in one of the pictures below. The recovery of that forest will take much, much longer.

Columns of the Giants, 2016

We stopped at a number of our favorite localities. Donnell Vista was not directly affected by the fire, but the viewpoint offered views of a major portion of the burned areas, including the slopes below the Dardanelles Crest, as seen in the first four pictures above. We also checked out Columns of the Giants, one of most awesome geological features along all of Highway 108. The trails and the bridge over the river were intact, but much of the forest and brush around the site were destroyed (see the pictures above and below for a comparison).

Columns of the Giants, August 1, 2019

The Dardanelle Resort was an especially sad sight. The historic old resort was obliterated, as were the slopes above. The resort had fallen into some disrepair over the years, but it had been purchased by new and ambitious owners only three months before the fire. They intend to rebuild, and a temporary trailer is already in place, serving as a temporary store.

The Dardanelle Resort 

Highway 108 near the Middle Fork of the Stanislaus River at the Old Dardanelle Bridge (which burned in the fire)

The historic 1933 Dardanelle Bridge was destroyed in the fire (photo below). It was apparently the last scissor truss-style bridge in the United States. It had been replaced by a more modern bridge around 1990 but was still maintained for walking. Ironically it was almost destroyed during the construction of the new bridge when some boulders from nearby blasting landed on the bridge, but it is unlikely to be replaced now.

The old abutments for the 1933 Dardanelle Bridge are left of the highway in the center of the photo

For all that was lost, much still remains. Highway 108 and other roads provided access for firefighters to battle the fire, so many sections of forest adjacent to the highway survived relatively unscathed. The firefighters were able in particular instances to set backfires just uphill from the highway that moved upslope, removing fuel for the oncoming main fire. In this way many of the cabins and developments were saved.

One of endangered developments was the High Sierra Institute at Baker Station. Originally a road maintenance facility, the cabins operate today as a research and educational center for the Yosemite Community College District which includes Columbia College, and my own institution, Modesto Junior College. Some trees on the property were lost, but the backfires preserved all of the buildings on the property.

Fires destroy, and fires renew. We live in a new climate regime, and we need to learn how to deal with this new world. Forests will regrow, but they will not be the forests that were lost. The ranges of the animals and plants are shifting northwards and upwards as the climate in California grows warmer and drier. Some organisms will be driven to extinction (the pika is in particular danger, as it lives at very high altitudes, and therefore has nowhere to retreat).

But there is also an emotional toll. We can't maintain the world as a museum where our favorite places remain, unaltered and unchanged by time. Change comes no matter what efforts we expend to preserve the past. Sometimes we can plan for the changes, such as developing master plans for parks and monuments, but wildfires are the bull in the china shop, causing destruction and change without pity or mercy. I grew up in Southern California and watched some of my favorite haunts in the San Gabriel Mountains disappear in wildfires. I moved to central California 30 years ago, and in that time have witnessed apocalyptic events like the Rim and Ferguson fires destroy large portions of the forests along and in the margins of Yosemite National Park.

As those of us who study geology know from our studies, there is nothing permanent about the world except for change. And sometimes the changes are tragic.

You Just Can't Take Sonora Pass for Granite: Travels Around the Sierra Nevada High Country

Sonora Pass in the Sierra Nevada is a sort of forgotten step-sister of the more famous Tioga Pass in Yosemite National Park. A paved road, State Highway 108, crosses the crest of the Sierra about forty miles north of Tioga, cresting out at 9,624 feet, but it sees far less traffic. There are, for instance, no national parks, no major ski areas (Dodge Ridge is thirty miles to the west), and no major resorts, and snowdrifts keep the pass closed for much of the year. But Sonora Pass is an incredible place to visit if you ever get a chance, and it makes for a nice loop trip out of the Central Valley, including Tioga on the way back.

The road is steep and winding towards the top, but the views are extraordinary. We are in the headwaters of the Stanislaus River, and the region was heavily glaciated during the ice ages, making for spectacular alpine scenery. But one thing seems to stand out as one approaches the summit. You can't take this pass for granite. At least not all of it. This bad pun can be understood in two ways: there is volcanic rock at the top of the pass, not granite, and what "granite" there is along the lower reaches isn't actually granite.

First off, there are lots of fine exposures of granitic rock below the pass, and along the highway for a considerable distance downstream to the west. But it is not technically granite. If one has had a basic earth science course, a person may have learned that there is granite, diorite and gabbro as the plutonic igneous rocks (light, medium, and dark). But if one takes physical geology or an upper division petrology course, one finds there are other rocks intermediate between granite and diorite. The differences come from the proportions of potassium feldspar, plagioclase feldspar, and quartz. As such, true "granite" is actually somewhat rare in the Sierra Nevada, perhaps accounting for 10% of the total. The most common rock is granodiorite, a granite-looking rock rich in plagioclase, but lacking in potassium feldspar.

I'm the first to admit that the difference to a layperson may seem trivial, but recognizing these differences allows researchers to draw many conclusions about the circumstances and timing of the intrusions that formed the backbone of the Sierra Nevada. And some of the other
"granitics" are truly beautiful rocks. At Sonora Pass, the common granitic rock is called the granodiorite of Topaz Lake, and it is one of the younger intrusions in the Sierra Nevada, having cooled about 89-93 million years ago. It has massively large crystals of potassium feldspar, 2-3 inches long, embedded in a groundmass (matrix) of smaller crystals of quartz and plagioclase. Such rocks with two distinct grain sizes are described as porphyritic. Glaciers have smoothed off the rock in many places ('glacial polish'), almost providing the effect of a polished countertop.

The other way that Sonora Pass cannot be taken for granite is the fact that the rocks at the pass are actually volcanic in nature. Between 11 and 9 million years ago, this area was an extensive volcanic center broadly similar to the one that exists today at Lassen Volcanic National Park, with andesitic stratovolcanoes, lava domes, and a modest caldera complex.

The volcanoes are long extinct, and glacial erosion has greatly modified their original outline. The mountains are striking if for no other reason than that they are different from many of the light-colored peaks of granitic rocks seen elsewhere. In a sense, they almost seem somber and dark. John Muir would no doubt have seen their beauty, but probably wouldn't have been inspired to call them the "Range of Light".

If you ever want to brag about your hiking exploits, but just don't have the energy, you can go to Sonora Pass, and wander a few yards up the trail that crosses the pass going north and south, perpendicular to the highway. That way, when people ask what you did last summer, you can truthfully say something like "I spent a bit of time on the Pacific Crest Trail"!

If you long to spend time in the Sierra Nevada, and just can't fathom the thought of fighting the crowds at Yosemite Valley and other parts of the national park, give Sonora Pass a look. I'm pretty sure you won't be disappointed. If you need a guide, my colleague Noah Hughes and I edited a field trip guide for the region for a meeting of the National Association of Geoscience Teachers in 2012, and the book we published is for sale (details are here; all proceeds support the scholarship program of the NAGT-Far Western Section).

The Other California: Highway 108 and Donnell Vista - like Yosemite, only with Volcanoes!

Those of you who've followed my blog over the years may remember that I produced a blog series called "The Other California" which existed long before any Toyota commercials with a similar slogan. I come back to it time and again when I find (or rediscover) those places that don't always show up on the tourist postcards, but which have incredible geology and are scenic to boot.

Today we are exploring a few corners of the Upper Stanislaus River drainage in the country north of Yosemite National Park. People from outside the region can be forgiven if they think that the Sierra Nevada is just Yosemite Valley, Sequoia National Park, and Lake Tahoe. The range is 400 miles long, and pretty much all of it is spectacular, except Yosemite and Sequoia are just a little more so. I cannot doubt that if Yosemite Valley didn't exist, the upper Stanislaus would have been one of California's national parks. In some ways, Sonora Pass and the upper Stanislaus are even more interesting in the geologic sense. The reason? Volcanoes.

Donnell Vista Point on Highway 108 about 18 miles above Pinecrest Lake and Strawberry is the site of today's exploration. The parking lot and quarter-mile trail to the viewpoint were recently renovated with funds provided by the America Recovery and Reinvestment Act. The old worn-out trail was resurfaced, and a new ADA compliant trail winds along the western part of the slope, providing some new views to the west.

The first thing one notices from the overlook at Donnell Vista is the deep U-shaped canyon occupied by the lake behind Donnell Reservoir. During the Pleistocene Ice Ages, rivers of ice repeatedly scoured the gorge below, with the last glacial stage ending only about 12,000 years ago. The ice exposed the underlying granite, forming steep cliffs and numerous small rounded asymmetical domes called roches moutonnées. Some nice examples of glacial polish can be found in the region.

The ice in most places removed a cover of volcanic lava flows and any soils were stripped away as well. As a result, wide areas of granitic rock are exposed, and the forest grows only in fractures and joints where bits of soil can accumulate.

Glaciers also scour out basins where lakes can subsequently form, but the lake below the view point is clearly not natural. It is Donnell Reservoir, constructed in 1957 by the Oakdale-South San Joaquin Irrigation district for storage of water for agricultural irrigation and power generation. It stores a bit more than 60,000 acre-feet of water which today is only used to generate electrical power. Storage for irrigation now takes place downstream in the much larger (and more controversial) New Melones Reservoir.

The high peaks to the north and east of Donnell Vista preserve the evidence of the volcanic activity that took place here 10-12 million years ago. The few remnants not stripped away by the ice form the mesa-like peaks on the skyline. When the volcanoes were active, the region would have looked a great deal like the Mt. Lassen volcanic center, which remains active today.

The lava flows filled a fault basin near the present-day Sierra Crest in the vicinity of Sonora Pass, and at times spilled over into the adjacent river valleys. One lava flow traveled nearly sixty miles to Knights Ferry in the Sierra foothills above Oakdale. The landscape surrounding the lava flow eroded away during the uplift of the Sierra Nevada block, leaving the lava flow as a prominent ridge called an inverted stream.

The upper drainage and headwaters of the Stanislaus River up to and over Sonora Pass offers up some fascinating geology. I helped edit a field guide of the geology of the region for a meeting of the National Association of Geoscience Teachers in 2012. It's for sale through Sunbelt Publications and the proceeds support scholarships for geology majors in California, Nevada and Hawaii. Get more information about the book here.

PS: Ron Schott has a great gigapan shot of the view from Donnell Vista at  http://www.gigapan.com/gigapans/114032