The Other California: Limekiln State Park, Part 1

What is the Other California? It's been a little while since I've posted on the subject, so here's what it is: an exploration of the lesser known places of our beautiful state, the places that you don't find on the postcards all that often; the places you visit when you've checked off that list of must-see spots like Yosemite or Death Valley. In today's post, we are taking a look at an interesting little beach in the southern part of the Big Sur Coast country: Limekiln State Park.

It's easy to miss while winding down the highway; focus too much on getting to the famous parks at the north end of Highway 1, and you might not see the turnoff at all. There is barely any parking available, so the beach is uncrowded. It's different from a lot of beaches in California; it has a good-sized creek that has littered the beach with large boulders of very attractive metamorphic and plutonic rocks. Does anyone see a face in the cliff?

Despite the late August visit, there was a lot of water for a central California River. A lot of them are dry by now. The mountains upstream reach a mile above sea level, and they catch a lot of rainfall. Enough sinks into the ground that springs keep the river flowing year-round. The babbling brook contrasts nicely with the crashing waves. I had a delightful time looking at chunks of gneiss, schist, marble, and granitic rock.

Highway 1 passes the park on a high bridge. Looking upstream, we can see that there might be a bit more to this park than a beach. For one thing, why in the world do they call it 'Limekiln'? What secrets lie up the the canyon? Keep an eye out for part 2!

Vagabonding across the 39th Parallel: Having a "Swell" Time on the Reef!

If you thought I was talking about sipping pina coladas on a beach in the Caribbean, well, think about nearly polar opposites. Hot, yes, but not tropical. We were in a very dry and remote place in central Utah. This is a continuation of our July journey through the American West, vagabonding across the 39th parallel. The swell is a huge domal uplift, and the reef is a long monocline. If there is one thing to say about driving along the 39th parallel, it is that the landscape never stays the same for very long.

Having crossed the transitional zone of the Wasatch Mountains, we had left behind the Basin and Range Province, and were now on the relatively stable crust of the Colorado Plateau. The plateau, as the name suggests, is mostly made of high flat mesas and buttes of horizontal sedimentary layers representing some 500 million years of earth history (with much older stuff buried beneath). Although mostly flat, the plateau region has been faulted here and there, and in places has been warped into a series of basins and broad domes. The San Rafael Swell is one such dome, and it is huge, 130 miles long and 70 miles across. From space, it is one of the most obvious structures in all of Utah (above).

A dome in this case refers to the shape of the sediments. They've been pushed up like a blister, but erosion has sheared off the upper layers, exposing the older layers underneath. As we left Salina, heading east on Interstate 70, the signs noted that there would be no services for the next 100 miles. That is the kind of sign that makes you look at the temperature and gas gauges...

At least the road was not as lonely as some of the others that we had been traveling. And because of the beautiful scenery, there are a number of turnouts with nice photo opportunities. The rocks are striking. They represent the entire Mesozoic Era (the age of the dinosaurs, basically), which lasted from 245 to 65 million years ago. Upper Paleozoic rocks are exposed in the core, while early Cenozoic rocks are found around the margins of the dome. All in all, some 8,000 feet of sedimentary layers can be seen while crossing the San Rafael Swell (the Grand Canyon has only 4,000 of Paleozoic layers, in comparison).

At the top of the post, I said we weren't on a tropical beach. That's not entirely true, it's just that the timing is off a little bit. Some of the oldest rocks exposed on the Swell were deposited on a tropical beach, and we had arrived just 300 million years too late to listen to the crashing waves.

The road passes through an hour of horizontal Permian and Triassic rocks, but at the eastern end of the Swell, the landscape goes crooked. The margin is marked by a massive monocline, an odd fold that has flat layers on one side, a flex in the middle and flat layers at a lower level. The effect is something like a stack of rugs draped over a step. We had reached the San Rafael Reef.

I know this photo below looks cockeyed, but if you look at the telephone poles on the ridge line, you'll realize the camera was level. It was the landscape that was bent. These monoclines were called reefs because they were barriers to east-west travel, just as a coral reef can block access to a harbor. Resistant sandstone layers eroded into teeth-like spikes separated by narrow slot canyons that made passage difficult. The freeway could only be constructed here by blasting a passage through the rock (if you click on the opening photo, you can see the cut at the bottom, with a red car for scale).

I heard braying while exploring the last rest stop, and saw a small herd of wild burros in the canyon below.

I pulled over as we passed the base of the monocline, and got some shots of the reef looking off to the south. One can see how difficult it might have been to find a passageway for a wagon or a Model T. The jagged white rocks are the Navajo Sandstone, the remains of a vast Jurassic dune sea that covered several states (the Navajo forms the cliffs of Zion National Park).

I've heard there are some nice canyons to explore in the area, as long as it is not raining. The slot canyons are notorious for trapping hikers.

The monoclines and domes of the San Rafael Swell were formed by compression of the crust, which was related to the Laramide Orogeny that took place around 80 to 50 million years ago. This event also had a lot to do with the formation of the Rocky Mountains. The monocline hides a large thrust fault in the deeply buried ancient crust, but the overlying sedimentary layers folded rather than split when the fault was active.

At the base of the reef, horizontal layers appeared again, including the very colorful Morrison formation, the one made famous by the many discoveries of dinosaurs, including the huge brontosaurs (yes, I know they aren't really called that), the allosaurs, and stegosaurs.

A few minutes later we arrived at the settlement of Green River (population 600 or so) to look for lunch. We decided not to eat at the "Rant Lounge", and settled instead for Arby's.

Vagabonding across the 39th Parallel: Who knew the hoodoo was in Castle Rock?

When you set out with no plan (or at least no detailed one), you just never know what is going to happen next, and what interesting places you can discover. We were vagabonding our way across the 39th parallel, and had reached the Wasatch Front in Utah. After looking at a great collection of artifacts and petroglyphs at Fremont Indian State Park, we were looking for a place to camp for the night. Signs at Fremont pointed down a dirt road to a campground. We checked it out, and what a surprise!

Castle Rock Campground is in a little hidden valley away from the noise of the interstate, and what a setting! The camp is surrounded by an intricate maze of hoodoos and high rhyolite cliffs. How did this landscape come about? And what is a hoodoo?

Hoodoos come about when relatively soft sediments include large boulders or capstone layers that can protect the underlying rock from being washed away. The effect produces towers and spires and a maze of winding narrow washes.

It is an otherworldly effect...kids would love this place, but keep a close eye on them! It's a lot easier to climb up these rocks than to climb down.

The photography opportunities are unending...the evening light was brilliant. Castle Rock is a spectacular place to camp. The camp itself is shaded by cottonwoods, and is nicely designed with well-spaced campsites. It was practically empty when we arrived (on a Friday!), but a number of people eventually showed up.

Once we climbed to a vantage point over the valley containing the campsites, we started to get curious about the rocks themselves. They weren't much like the ones exposed at the museum only a mile away, and the rhyolite cliffs were hundreds of feet high, unlike the cliffs down lower, which were only a few tens of feet high.

The hoodoos are composed of conglomerate, sandstone, and siltstone, the kinds of sediment associated with deposition by rivers and streams in alluvial fans and shallow lakes. The coarseness of the sediments suggests a local source area. A few light-colored ash layers in the sediments provide the opportunity to date the sediments.

In the last post, we discussed the eruption of the Joe Lott tuff, which took place 19 or so million years ago. Soon after the blasts, volcanism declined, and the region began to stretch. The onset of basin and range extension caused numerous fault valleys to develop, and these local basins started filling with sediments washed from the adjacent uplifted mountains. The layers at Castle Rock were laid down between about 14 to 5 million years ago, on top of the tuff deposits.

At the upper end of the camp, something else had happened. The layers weren't horizontal anymore, they were dipping steeply to the north, right next to the high cliffs of rhyolite. I wanted to investigate the contact to see what was going on.

But the sun was dropping below the horizon, so we would have to wait until the next day.

We went to bed under a full moon.

The next morning we scrambled up some rough topography to try and get a view of the contact zone.

It turns out that the contact is a fault zone, and that the tilted layers represent a drag fold caused by the downward movement of the valley block. The fault is a normal fault (the headwall has dropped relative to the footwall), the kind caused by extensional forces, which is what would be expected here.

The rhyolite was just as thin as it was in other parts of the state park, but because it had been tilted, it appeared to be much thicker. The deformation caused cracks and fractures in the rhyolite that developed into strange erosional forms like the hollows, arches, and caves of tafoni weathering.

It was great place to explore! After a few hours we packed and hit the road, heading east on Interstate 70, wondering what would come next. The answer wasn't long in coming, but that's another post!

For more information on the geology at Castle Rock Campground, check out:
http://geology.utah.gov/surveynotes/geosights/castlerock.htm
and chapter 12 of Geology Underfoot in Southern Utah, by Orndorff, Wieder, and Futey

Earthquake Swarm near Pinnacles National Monument in California

Source: U.S. Geological Survey (http://earthquake.usgs.gov/earthquakes/recenteqscanv/FaultMaps/121-37.html)

An earthquake swarm is affecting the San Andreas fault system in the Pinnacles National Monument region of the Central California Coast Ranges. The biggest event thus far is a magnitude 4.6 at a depth of 7.6 km, with other significant quakes measuring 3.2, 3.2, 3.3, 3.6, and 3.3. There have been nearly 100 instrumentally recorded quakes between magnitude 1 and 3. The quakes are taking place in a complex region of the fault system where the Calaveras, Hayward and San Andreas faults merge into a single fault. This area is notable because the San Andreas fault is creeping, rather than sticking, meaning that the fault moves constantly (a few millimeters a year) instead of storing up stress and producing monster quakes like it does both to the north and to the south.

Road damage from fault creep on the San Andreas fault near the earthquake epicenter. This is a 2010 picture; the damage was NOT caused by the earthquakes today

This is not an unusual pattern; flurries of similar earthquakes have occurred in the Pinnacles area in 1951, 1972, 1982, 1995, and 2004. If the pattern holds true, the quakes will decline in number and size over the next few days. There is always a small chance that the activity (including the 3.9 quake in San Leandro earlier this week) is a precursor to a much larger earthquake, such as the magnitude 7 event that took place on the Hayward fault in 1868, which killed two dozen people. A recurrence of the 1868 earthquake would cause serious damage and destruction in the East Bay region.

Events like these are reminders that we Californians are living in earthquake country, and that we need to be prepared for larger catastrophic seismic events. It is a virtual certaintly that the state will be rocked by magnitude 7+ events in the next few decades, and some of these earthquakes will affect urban regions. One should always have emergency supplies available, and a plan for what to do in the event of a major earthquake.

Shutter ridge on the San Andreas fault near the earthquake swarm epicenter. The fault follows the fence line.

Vagabonding across the 39th Parallel: We Reach the Wasatch Front, Finding Geologic and Archaeological Violence

Vagabonding across the 39th Parallel is an informal exploration of the geology of an interesting slice of the American West that I traveled in July this year. In the previous set of posts, we were crossing the Basin and Range Province, an exceedingly lonely region. We reached western Utah, and things started to change. Snowcapped mountains appeared on the far horizon, and the landscape became greener. Agricultural fields appeared, and then, a superhighway. Traffic was moving at 80 mph on Interstate 15, and there was a lot of it. We had reached the Wasatch Front.

The Wasatch Range is the transition zone between the Basin and Range, the Colorado Plateau, and the Rocky Mountains. Faults slice through the mountains, but the intervening valleys are not as deep as they are farther west. There is a feeling (not necessarily justified) here of a certain degree of geological stability. The sedimentary layers that are exposed in the area are generally less deformed, and form plateaus and mesas a short distance to the east. That's not to say that there is no activity. The Wasatch Front is a major seismic zone, and there is an uncomfortable possibility of large earthquakes along the frontal fault system.

We turned off Interstate 15, and headed more or less east on Interstate 70. Our rules of the road for this trip dictated that we did not plan too far ahead, so even though it was late in the afternoon, we still didn't know where we would be stopping for the night. We were discussing where the next KOA might be when we saw a turnoff that said "Fremont Indian State Park". What the heck, let's check it out, we thought.

Did I say that the Wasatch seemed like a stable place? A close look quickly reveals a past history of great violence. Those innocuous-looking cliffs at that park (in the picture at the top, and below), which could be mistaken at a distance for sandstone, turn out on close inspection to be rhyolite tuff.

Rhyolite is the most viscous of volcanic lavas, meaning that it flows almost not at all. It comes out of ground with a consistency something like toothpaste. But if the rhyolite is charged with dissolved gases, it doesn't flow at all; it explodes with great violence. The lava is pulverized into dust particles as it bursts into the atmosphere. The scale of rhyolitic eruptions can be huge, sometimes involving dozens, even hundreds of cubic miles of material. As the eruption wanes, the crust of the earth collapses into the void created by the explosion of ash, forming a huge pit called a caldera. The holes can be many miles across. Hot ash falling to the ground near the caldera often remelts, forming a solid rock layer called a welded tuff, or ignimbrite.

At Fremont Indian State Park in Utah, just such an eruption took place around 19 million years ago, forming the Mount Belknap caldera several miles away to the southeast. The welded rhyolite ash is called the Joe Lott tuff. The volume of the eruption was nearly 100 cubic miles, which puts this eruption in the same league as those that formed the Yellowstone caldera in Wyoming, or the Long Valley caldera at Mammoth Lakes in California.

The rhyolite cliffs in the vicinity of Fremont Indian State Park were valuable to the original inhabitants of the region for at least two obvious reasons. Rhyolite often forms obsidian (volcanic glass), which could be formed into sharp tools like arrowheads, spear points, or axes. Cultures with access to obsidian deposits had a valuable and marketable commodity.

The welded tuff cliffs were also relatively soft and easily chipped. The cliffs were an irresistible canvas for chipped rock art, that is, petroglyphs. There are hundreds of them in the vicinity of the park, and a short trail from the museum provides easy access to some excellent examples.

The Fremont people were an enigmatic culture that lived in this area from about 400 to 1300 AD. They didn't construct massive cliff dwellings like those of the late Ancestral Pueblo people farther south at places like Mesa Verde. They lived in less easily preserved pithouses, and farmed maize and beans in a swath of land across central Utah and easternmost Nevada. Their artwork is distinctive and very mystical and symbolic. The meaning of many of the figures is not clear to anthropologists, but I imagine that they are quite obvious to a number of the existing Pueblo cultures who are probably their descendants.

The wavy lines are often interpreted as snakes, although I have seen some speculation that these lines may actually record a memory of violent earthquakes (recall the proximity of the Wasatch fault zones). The petroglyphs on the left side of the picture below are thought to be bird tracks or sprouting corn.

Do you recall a Vietnam War era quote about destroying a village in order to save it? Here at Fremont Indian State Park, they had to save a village in order to destroy it. When the roadbuilders were putting in the Interstate, they had to cut through hill in the picture below. As they started, they discovered a huge Fremont village, the largest ever found. The freeway was going to destroy it. It was excavated, and the artifacts that were recovered became the basis for the collection at the museum in Fremont Indian State Park. I somehow found this conflicting juxtaposition of cultures disturbing.

We had seen a sign that there was camping across the highway. We drove over to check it out; we were in for a big surprise! That will be covered in the next blogpost...

For more information about Fremont Indian State Park:
Park website: http://stateparks.utah.gov/parks/fremont
Park brochure: http://static.stateparks.utah.gov/docs/FremontIndianBrochure.pdf
Chapter 13 of Geology Underfoot in Southern Utah by Orndorff, Wieder, and Futey

Accretionary Wedge #37: Sexy geology and discrepant outcrops, and the answer to Tuesday's mystery photo

Photo by Mrs. Geotripper

This month's Accretionary Wedge (#37) is sponsored by Lockwood at Outside the Interzone, and involves "sexy geology". To be more precise, it is about "geology that makes your heart race, your pupils dilate. Rocks and exposures that make you feel woozy and warm. Structures and concepts that make your skin alternately sweaty and covered with goosebumps. Places you've visited, read about, or seen photos of that make you feel weak-kneed, and induce a pit in your stomach".

Geotripper checks out a really cool outcrop (photo by Mrs. Geotripper)

There are all kinds of such outcrops and choosing is hard, so I settled for the last outcrop I saw that brought on a visceral response. It was last Saturday, while I was checking out a possible field trip route in Southern California. The outcrop also happens to be the answer to Tuesday's mystery photo. Read on!

The Monterey Shale is usually white; why is it gray here?

The Monterey Shale (or Modelo Formation) is a deepwater deposit of shale, sand and diatomaceous earth that is exposed widely along the California Coast. It was deposited in Miocene basins adjacent to the San Andreas fault, and the rock is unusually rich in organic material. When buried deeply in the crust, long slow heating causes the organic material to simmer into petroleum and natural gas. As such, the Monterey has been the source rock for billions of barrels of California oil.

So what was the mystery rock? I was educated as a geologist, not a teacher, so it took a few years before I heard about the concept of discrepant events in education. A Discrepant Event is something that "surprises, startles, puzzles, or astonishes the observer. Often, a discrepant event is one that does not appear to follow basic "rules of nature" and the outcome of a discrepant event is unexpected or contrary to what one would have predicted". Well, Tuesday's mystery rock wasn't a discrepant "event", it was a discrepant outcrop. The result looks like something familiar, but is far from normal.

I suggested that readers follow their intuition, and that their answers would be "sort of half right". Most respondents suggested that they were looking at obsidian (above), and some kind of tuff or scoria (below). They were sort of half right. The problem is that these rocks are not volcanic at all. Brian, at my Google+ page maybe came the closest by guessing that these were fulgerites, fused rocks caused by a lightning strike.

Much of the Monterey Shale is composed of silica, and much of the silica is saturated with oil. Perhaps you might wonder what would happen if the rock ignited? It could have been a lightning strike. It could have been a forest fire. In any case, the rock burned underground, and reached temperatures sufficient to melt the shale into an obsidian-like rock. In places, gas bubbles produced the vesicular texture that resembles tuff or scoria. Oxidation of the rock produced a rainbow of red, purple, orange and yellow rock (the quarry across the road apparently is producing colorful decorative stone). Native Americans have made use of the glass for thousands of years for spear and arrow points.

So, is this rock igneous, sedimentary or metamorphic? Some sources refer to combustion metamorphism, others refer to fused shale. No one talks about magma. In any case, I found the rock fascinating. Even downright sexy.

More information on this cool outcrop can found here. It is located on Grimes Canyon Road just a few miles south of Fillmore, California.

A Mystery Photo for a Tuesday (and a bonus mystery photo)

Hi all! I've been away, and out of contact with the world for a few days. Is anything going on geologically? OK, yes, I did actually hear about the quake in Virginia, but not until many hours later...

Anyway, I was doing some field trip research in Southern California. Even though I grew up down that way, and worked at Santa Barbara City College for four years, I saw a lot of new and very interesting territory. Expect to see some new "Other California" posts over the next few weeks.

In the meantime, here is a mystery rock for you to identify. I can't give you too many clues, other than to say to trust your intuition, and realize that the answer will only be sort of half right

And here is a second handful of mystery samples to identify, from the same outcrop.

So, what are these rocks, and how did they form?