The Yosemite No One Sees in Summer...the Merced River Canyon

The drought in California is horrific. It is quite probably the worst drought in centuries, but we received a slight respite in the form of showers and snow during the last part of March and early April. It was a drop in the bucket towards relieving the huge water deficit that has built up in the last few years, but it gave a shot of energy to the seedlings of grasses and wildflowers. They perhaps should have sprouted and grown months ago, and they will be dried out in a few short weeks, but this week, the Sierra Nevada foothills were alive with color.

We were on our way to Yosemite Valley for our geology field studies course last Saturday, and I joked (only in half-jest) that the students had to "earn" the right to learn the geology of Yosemite Valley by first exploring the canyon of the Merced River. We had to prepare ourselves by undertaking a journey through the rocks that predate the granitic rocks that form the walls of the iconic valley. Our route took us through the foothill towns of Snelling and Hornitos, and then we drove up Highway 140 through Mariposa, over Midpines Summit and down into the deep gorge of the Merced River (originally the "Rio de Nuestra Señora de la Merced (River of Our Lady of Mercy)".

Highway 140 winds back and forth through a series of metamorphic terranes, bands of deformed and twisted rocks that traveled across the Pacific Ocean to be mashed into the western edge of the North American Continent. The rocks include slate, schist, marble, phyllite, quartzite and greenstone. These were the ancient rocks (between 600 and 200 million years old) that were intruded by the granitic rocks that eventually were exposed and eroded to form the dramatic cliffs of Yosemite Valley.

The Sierra Nevada is a huge westward tilted block. The slope has allowed the rivers draining the mountain range to carve deep gorges, some deeper than the Grand Canyon (Kings Canyon to the south is about 8,000 feet deep!). The depth of the Merced is more like 2,000 to 3,000 feet deep downstream of Yosemite, and in any other setting in most any other state, this would be enough for the establishment of national parks and the like. Instead, it is "just" the preliminary canyon one must pass through before arriving at Yosemite.

The carving of such deep canyons can have serious geologic consequences for society. The slopes of such canyons are inherently unstable, and mass wasting (landsliding) is a constant hazard. The building of roads and railways adds to the instability by undercutting the already steep slopes. Such is the case with Highway 140. CalTrans has struggled for years to prevent the collapse of a slope near the village of El Portal. In 2006, the slope flicked away the mitigation efforts and collapsed onto 600 feet of highway. The Ferguson Slide, as it is called, closed the highway for months and caused economic hardship for the surrounding communities. Two temporary bridges were constructed to cross the river and circumvent the huge slump. Decisions have yet to be reached regarding the permanent disposition of the highway.

The Ferguson Slide. 600 feet of Highway 140 is buried under the rocks.

As we drove deeper into the Merced River Canyon, the slopes seemed to come alive in orange and gold. The California Poppies have reached the zenith of their blooming cycle. In contrast to my previous gloom and doom post regarding fires, rejuvenation does indeed occur, as many of these slopes have been cleared of brush and chaparral by repeated wildfires, allowing for dense concentrations of wildflowers.

We passed El Portal, and then the Yosemite View Lodge. The name is not totally dishonest; the boundary of the national park does indeed lie a few yards east of the hotel complex, so the view of the granite slope beyond is indeed a view of Yosemite. But it is not yet the iconic valley with Half Dome and El Capitan and Yosemite Falls. It is pretty, though, and the Merced River makes a dramatic dash through the maze of gigantic fallen boulders.

 We arrived at the park entrance station, drove a few more miles, and made our last stop before Yosemite Valley. It was another site of mass wasting, but this time it was a rockfall, and it included granitic rock instead of metamorphic material. The so-called Cookie Slide took place in 1982, and involved around 100,000 cubic yards of material that bounced and fell down the slope onto Highway 140. Once again, the road was blocked for weeks.

 The size of some of the fallen blocks is astonishing. It's hard to see how a block like the one in the picture below held together during the downhill descent.

The rocks are part of an intrusive series called the El Capitan granite, which was intruded about 103 million years ago. A contemporaneous intrusion of dioritic rock lead to some co-mingling of magmas, including the enclave of darker rock in the granite (below).

I've always thought of granite as a particularly beautiful rock. The sparkling mass of quartz (glassy gray color), orthoclase feldspar (white grains), and biotite mica is pleasing to the eye, and tells an odd story: Yellowstone National Park, off in Wyoming, sits on top of a huge magma chamber that may one day explode again (but not tomorrow). In Yosemite, we are sitting within a former magma chamber, under the volcano. As such we are exploring the inner depths of an extensive magma system, brought to light by long periods of uplift and erosion.

In a coming post, we'll see how Yosemite looked on Saturday.

Spring arrives in the Sierra Nevada Foothills (and a gratuitous mammal photo)

A long work week, and then another family gathering, this time in Porterville in the southern part of California's Great Valley. We couldn't resist the desire to see what was happening in the Sierra Nevada foothills, so we headed up a new road for us, Yokohl Valley Road.

The road goes nowhere in particular, joining the valley with roads leading to Success Reservoir and Balch Park in the Sierra high country south of Sequoia National Park. Mostly it provides access to a number of ranches.

Descending some steep switchbacks below the pass, we began encountering wildflowers at about the 2,000 foot level. I've seen more fiddlenecks than I recall seeing in the past. Many yellow slopes so far this year have been fiddlenecks instead of poppies. That's not to say we didn't see poppies; they were abundant in a few places, along with some beautiful bush lupines.

 There were the usual unidentified small flowers that I the geologist can never remember a name for...

And more bush lupine providing a foreground for Yokohl Valley Road in the distance. There was some interesting geology along our route, which will likely be the basis of another "Other California" post in the near future.

The spring flower season comes and goes quickly in the Sierra foothills and Great Valley. It's building to a climax, and I hope I can think of enough excuses to hit the road again soon.

Oh, and as promised, a gratuitous mammal photo. This little guy was looking pretty well fed, but someone should warn him about the coyote that was lurking around the next bend in the road....

Life from an Ant's Point of View: Springtime in the Sierra Foothills

I find that the average lifespan of an ant is something like a month or two. So bear with me while I have some silly thoughts about ant culture. What must the average ant think when it sees the explosion of color above when spring arrives in Sierra Nevada foothills? Probably not much, but it's fun to imagine the legends they might pass on down through the generations. "Your great aunt ant? Remember her? She was so old: four months. She told us of a time when the brown stalks were green and alive with color, and there was sweet nectar in the midst of the plants, and it was a time of richness, never to be forgotten in our legends"

I was off on another adventure this weekend. It was work, actually, helping a relative move in Southern California. I've been down Highway 99 probably 150 times in the last 25 years, so when we woke up this morning, the San Bernardino to Bakersfield drive prior to following Highway 99 to our home near Modesto just did not seem all that...appealing.

Luckily, we did not have a strict schedule, so we got very creative, seeing if we could spend as little time as possible on Highways 58, 14 and 138, and despite all my explorations, we found four roads that I have never traveled, or hadn't traveled in more than 25 years. They included Lone Pine Canyon along the San Andreas fault near Cajon Pass, Backus Road and Willow Springs Road outside of Mojave, Woodford-Tehachapi Road at the top of the Tehachapi Mountains, and Arvin Road at the bottom of the Tehachapi Mountains. Four adventures in one day, capped by the 200 mile drive on Highway 99 to Modesto. We had the most fun on the first part...

I took 200 pictures, and Mrs. Geotripper took even more, so there are probably a few more posts coming in the next few days, discussing faults, wind energy, trains, and wildflowers. Since wildflowers are the subject of today's photos, I can report that spring has arrived at the very south end of the Great Valley, and there are some beautiful sights along Highway 223 out of Arvin to the junction with Highway 58. It's been a dry year, so I don't know how the long the show will last. I don't know how often people find a reason to visit Arvin, but this is a really good time to head there. More coming on wildflowers!

Meanwhile, please enjoy these few shots of life from an ant's point of view....

A Fool for Fiddlenecks and Lover of Lupines

Not very geological, I suppose, but sometimes my travels and interests spill over into the biological realm. Part of the fun of springtime in the Sierra Nevada is the profusion of flowers that emerge for a couple of weeks. It doesn't take long before they dry out and lay down seed for next year, but the geography keeps the show going all summer. The Sierra mountain block rises gently to the east, and as conditions dry out in the foothills, the snow is only starting to melt in the high country. There are flowers to be seen somewhere in the mountains all summer long.

One of my early-season favorites are the Fiddlenecks in the genus Amsinckia, a small flower that blooms especially well along roadsides and disturbed surfaces in the foothills. There are around a dozen species across the American West. They're poisonous to livestock and considered a weed by some, but parts of some species were utilized by Native Americans for food and medicinal purposes. One of my other favorites is the Lupine (genus Lupinus), which grows at many elevations in the Sierra, and for that matter throughout much of the world (there are hundreds of species). Like the Fiddlenecks, it is poisonous to cattle and can sometimes be considered a noxious weed. On the other hand, some species produce a nutritious edible seed and are considered an alternative to soy beans. They also fix nitrogen in the soil, allowing other species to colonize.

The other pretty flower I noticed in this early part of the spring bloom was the one below, but I don't know what it is. Any of my flower-expert readers gonna tell me? Some kind of Brodiaea?

The Other California: The Day of the Fiddlenecks (a trip in the Mother Lode)

The Other California is my continuing exploration of the places in our state that don't tend to show up on the postcards, and are missed by most of the visitors. It's the first day of spring and we headed up into the Sierra Nevada foothills to seek out the Golden Poppy, which should be blooming explosively on the grassy slopes by now. We traveled east on Highway 132 out of Waterford towards the Gold-Rush-era town of La Grange. The poppies hadn't popped out in the lower foothill areas, but the slopes were alive with one of my favorite flowers, the Fiddleneck (Amsinckia). The shape of the flower is reminiscent of the head of a violin.

Amsinckia was utilized as a medicine and a food source by Native Americans, but the seeds and foliage are toxic to cattle. Today, for us, it was a beautiful splash of color along the slopes of the Tuolumne River, which were following out of the Central Valley.

Upstream, the first bedrock outcrops we encountered were low cliffs of rhyolitic ash of the Valley Springs formation. This gentle, quiet landscape was the scene of great violence between 22 and 28 million years ago, as huge calderas to the east exploded out vast amounts of pulverized rock and sent clouds rolling down the slopes of what would one day be the western Sierra Nevada. The rock is solid enough to form cliffs, but is easily shaped, so it was ideal for use as a building stone in the towns of the Mother Lode.

We passed through the quiet village of La Grange, looking at the 1875-vintage schoolhouse and cemetery, and a short distance east we encountered some of the evidence of gold mining (below). The sediments covering the surface were washed away to get at gold particles trapped in the small fissures and cracks in the bedrock below. Sometimes hoses were used. Downstream, where the sediments were deeper, giant dredges were used (these methods will be discussed in later posts). One of the dredges used in the area sits abandoned in a meadow just south of La Grange.

A bit east of the hydraulic pits, the old metamorphic rock of the Foothills Terrane start peeking through the soil cover. These so-called "tombstone rocks" are slate and phyllite that originated as mud and silt on the ocean floor which were accreted to the western edge of the North American continent in Mesozoic time.

Some of the rocks include metavolcanic rocks and an occasional metaconglomerate (picture below, very small penny for scale). These rocks are far more resistant to erosion, and form long high north-trending ridges in the western Mother Lode. We found a delightful new pathway over the metavolcanic ridges from Don Pedro Reservoir to the village of Moccasin along Marshes Flat Road. On this spring day, greenery was everywhere, and most of the gullies had streams flowing.

Did we find poppies? They aren't widespread just yet, but a few beautiful patches showed up along Marshes Flat road. There will be a great many more in the coming weeks. If you are in the area, make time to check it out!

For an excellent road guide to some of the areas covered in this post, and for a discussion of remediation efforts along the Tuolumne River region, check out this guide from the National Association of Geoscience Teachers and Columbia College.