Pleistocene bones abound beneath the Fairmead landfill near Chowchilla. See them at the Fossil Discovery Center of Madera County. Photos by Andrew Alden

My previous side trips from I-5 have involved rocks, but that's not all there is to geology. This suggested route, an alternative to taking I-5 straight south to Los Angeles, will expose you to the southern Great Valley's hydrology and many excellent, recently excavated fossils.

Start by exiting at Santa Nella — not to patronize the garish set of businesses there, but to take state route 152 east. You'll go all the way across the valley to Route 99, then south from there to the "Grapevine".

The first thing you'll notice, if you haven't already, is the profusion of canals in the Valley. They come in all sizes, ranging from the Edmund G. Brown Aqueduct (that's the first one you cross) down to uncountable numbers of field ditches. There are natural streams, but most of the water you'll see is in canals. This one runs parallel to the San Joaquin River about 6 miles west of Dos Palos Y.

Right next to it, the river that gave its name to the San Joaquin Valley was a sandy ditch in March during the rainy season. In good weather you'll be able to see mountains wherever you are, either the Coast Range on the west or the Sierra Nevada on the east (as seen here). I believe that there is no place in California where mountains are not visible if the air is clear.

The far end of route 152 meets Route 99. I recommend the old-timey charm of Chowchilla just north of here for a road stop, but otherwise you'll turn south on 99 and take the very first exit to the Fossil Discovery Center of Madera County.

Photo courtesy Tsing Bardin

The center is across the road from a sanitary landfill, and for a good reason: in 1996, diggers at the new Fairmead landfill uncovered a complete mammoth tusk. Soon it was realized that the site contained a world-class Irvingtonian fossil fauna dating from the mid-Pleistocene about half a million years ago. (There's a Bay Area connection here: the Irvingtonian is named for the wonderful bone beds unearthed in the East Bay's Irvington district during freeway construction in the 1940s.)

A paleontological foundation was set up and scientific ties established at nearby Cal State Fresno. Whenever the landfill operators open up a new pit, fossil scientists are on hand to harvest what they can. Bones of mammoths, wolves, sabertooth cats, horses, camels, ground sloths and many smaller creatures are stockpiled and studied at leisure between digs. The Fossil Discovery Center opened its doors in late 2010 and makes an excellent visit whatever your level of interest or expertise. Its outdoor "Pleistocene Water Source" exhibit makes it easy to imagine the lush scene in ancient times.

You can sit out back, next to the fossil washing station, and cast your eye over the surrounding land. I was told that the center has options on some of this acreage, where thousands more fossils surely lie in wait.

Eventually you'll need to return to 99 and resume your journey. Another stop you should consider is in Bakersfield, where less than 5 miles east of the road on Stockdale Highway is the city's gracious new Riverwalk Park on the Kern River, which is still a vigorous stream here.

Bakersfield has a lot going on. Another spot to consider visiting is the Buena Vista Museum of Natural History, home of superb fossils from nearby Sharktooth Hill.

The Greathouse Portal Visitor Center, inside the former Hazel-Atlas sand mine, is open again after five years. Photos by Andrew Alden

With California's state parks under threat of imminent closure, the East Bay Regional Park District is a bright spot for naturegoers. Careful management has maintained steady funding in hard times, and this summer EBRPD's Black Diamond Mines Regional Preserve promises to be a well-attended place—especially with the long-awaited reopening of its underground Greathouse Visitor Center.

Black Diamond is named for its history as California's largest coal district, starting in the 1850s. Coal was a prerequisite of 19th-century technology, and its discovery in the hills south of Antioch helped propel the new state of California to prosperity. It wasn't great coal, being classified as lignite or the lowest grade of coal, but it was good enough to do the job. Several mining towns sprang up here, and for a while this was the biggest settlement in Contra Costa County.

Fragments of Black Diamond's low-grade lignite coal can still be found in the tailings piles.

The coal didn't run out, but by the 1890s better coal was available from elsewhere so the mines shut down soon after. Next came the exploitation of the premium quartz sand beds beneath the coal. The sand mines supplied glassmakers in Oakland and steelmakers in Pittsburg from the 1920s to the late 1940s. That was when the Greathouse underground chamber was created, in the Hazel-Atlas sand mine. The Regional Parks District repurposed it as a visitor center in the 1970s, but storm damage shut it down in 2007. After five years of painstaking rehab, the room is receiving visitors again every weekend at no charge.

The old mining district is hidden from the riverside sprawl of Antioch behind a narrow canyon and oak-dotted hills. Driving through the canyon is like leaving the 21st century behind.

Inside, the vegetation is more lush on the higher hills, and miles of trails snake through the country. The area is notable for wildlife and plant species, but geologists find it notable too.

The bones of the hills are relatively young sedimentary rocks that are well exposed here. They extend all the way across the Central Valley in the subsurface. I look forward to showing you more as I explore this beautiful place.

Protecting blue-green Rodeo Lagoon from the green-blue Pacific, Rodeo Beach displays unusual materials in its unusual setting. Photos by Andrew Alden

The strait called the Golden Gate has beaches on both sides of its seaward end. On the south side, in San Francisco, are Baker Beach and Ocean Beach, which are made of fine sand derived mostly from the Sierra Nevada. On the north side in Marin County is little Rodeo Beach, which is not. Rodeo Beach is small but has a lot to see.

Rodeo Beach is next to old Fort Cronkhite in the Golden Gate National Recreation Area, situated between the sea and the valley of Rodeo Creek. The beach qualifies as a bar, the geographer's term for a pile of sediment that crosses the mouth of a river. As you can see in the top photo, Rodeo Creek is dammed behind the beach to form Rodeo Lagoon, but some of the water from the lagoon manages to spill across the beach at its north (left) end into Rodeo Cove.

Rodeo Creek supplies no sediment to the shoreline. Instead, the beach's sand and gravel is manufactured on the spot from the local bedrock of the Franciscan Complex, which crops out in steep coastal bluffs on either side. Before you study the beach itself, take a look at these rocks. There are three main Franciscan rock types at Rodeo Beach that you can easily distinguish: on the south side (see below) are chert and basalt and on the north side is sandstone.

View south of Rodeo Beach toward Point Bonita

Chert is the most obvious of the three, a hard, flinty stone arranged in hundreds of thin layers. This is the same deep-sea ribbon chert visible along Conzelman Road as you arrive through the Marin Headlands, but here parts of it have been turned green and even bluish colors by the pressure and chemical action of metamorphism.

Basalt here is not the black lava you might expect in Hawaii or the Cascade volcanoes. It's largely deep-sea pillow lava that also has been metamorphosed into greenstone. The original pillow shapes persist in some places here.

The sandstone of the northern bluffs is not the red or brown rock of the Grand Canyon, but a dark grit with its own metamorphic overprint. Of these three rocks, basalt is the weakest, the sandstone grains are the hardest and the chert is the toughest. In Rodeo Cove, the vigorous Pacific surf tosses and sweeps and grinds them together, turning out batch after batch of coarse dark sand mixed with polished chert pebbles. The north end of the beach is the best place to admire (and not collect) this exquisite gravel.

Geologists have studied this sediment closely and matched its ingredients to nearby rocks, although one rare constituent used to puzzle them: round pebbles of translucent carnelian, a red-orange gemstone. In Geology of the San Francisco Bay Region, Doris Sloan states that in the winter of 1967 after an especially strong storm, the outflow channel from Rodeo Lagoon dug its way to basalt bedrock six feet down. In that deeply buried stone the source of the carnelian grains was found. They had formed when bubbles in the lava filled with silica—in geologist's jargon, they were amygdules or mineral-filled vesicles.

Carnelian in a ring and amygdules in basalt, Berkeley Hills

Ever since learning this, I've watched for another such coincidence of storm and tide, although a lifetime might not be sufficient. As could be said of various things, the most severe times may produce the most sublime experiences.

Carbon dioxide streams into a pond near the Sulphur Bank mine at Clear Lake. Volcanic gases are a very small factor in the atmospheric system that controls world climate. Photo by Andrew Alden

Here in the Bay Area, it's easy to find volcanic influences: Just visit one of our many hot springs, or Clear Lake, where I took this photo. These gassy springs that are bubbling with carbon dioxide are associated with young magma underneath the northern Coast Range. Many people believe that volcanic emissions of CO₂ are a much greater influence on world climate than CO₂ from human activities. Is that right?

The answer is no. It's a persistent delusion, similar to the idea that U.S. foreign aid is responsible for the national debt. Volcanoes erupt because of water vapor dissolved in lava. Volcanoes do release CO₂, sometimes a great deal of it, but humans have been outdoing nature for a long time. Geoscientists have made many estimates of global volcanic CO₂ production because it's one of those important numbers in the long-term, geologic carbon cycle. Plate tectonics carries buried carbon down into the deep Earth, and volcanoes burp it back up again.

At the global scale, the natural carbon cycle is slow and gentle, although the numbers may seem large: Volcanoes on land and under the sea release somewhere between 150 and 260 million tons of CO₂ per year. However, human emissions of this greenhouse gas are around 35 billion-with-a-B tons a year when you add up burning oil and gas, manufacturing cement, running coal-fired power plants, and changes in land use like digging up soil and cutting down forests. We are a preposterously greater emitter of CO₂ — two orders of magnitude greater. And while volcanoes are pretty steady, humans are getting worse and worse.

Volcanologist Terry Gerlach, of the U.S. Geological Survey, has been publicizing this inconvenient truth. In a 2011 article in Eos, aimed at scientists, he puts the numbers in a geological context. If volcanoes had to match the human output, he says, it would require one or more Yellowstone-size supereruptions every year. Put another way, there would have to be ten Mount St. Helens eruptions every single day. (By the law of averages the U.S. would get one of these about once a week.) I say, lie back in your local hot spring and rejoice that CO₂ emissions are a problem that human ingenuity and action can address.

Learn more about the basics of volcanic gases at Volcano World.

The Sutter Buttes are an isolated volcanic center surrounded by super-flat bottomland of the Sacramento Valley. All photos by Andrew Alden

If it's a fine day and you have a couple of hours to spare on your drive north, why not see one of the curiosities of California and take a spin around the Sutter Buttes, also known as the world's smallest mountain range.

The Buttes are a compact clump of rocky crags placed smack in the middle of the flat Sacramento Valley. If you know where to look on a clear day, you can first spot them from I-505 as you drive north just north of Winters, some 40 miles off. They're like a mirage, glimpsed through the distant trees and silos, that soon vanishes as an imperceptible rise cuts them off. Otherwise their first appearance is a vision dead ahead as you exit the rounded, dreamlike Dunnigan Hills just before joining I-5. On many hazy days you may catch the barest outline of the Buttes' fairytale-steep peaks and wonder if you're seeing anything at all.

The Sutter Buttes are the remains of a young volcanic center that flourished here between about 1.5 and 1.3 million years ago, during the Pleistocene Epoch. On the geologic map below (derived from the California Geological Survey's interactive state geologic map) its bulls-eye shape is distinct.

Rock units are as follows: Qv, lava plugs and domes; Qv^p, volcanic flows; E and Ku, Eocene and Cretaceous sedimentary rocks.

A central set of lava plugs and domes (Qv) is surrounded by an apron of volcanic flows of lava and debris (Qv^p). After the eruptions stopped, erosion uncovered the older sedimentary rocks (E and Ku) that were folded upward by the rising magma. These folded older rocks are prime sites for natural gas wells. In the 1920s the volcanologist Howel Williams, a native of Wales, gave names to these parts that were inspired by Medieval castles: Qv is the Castellated Core, Qv^p is the Rampart and the soft old rocks between make up the Moat. See more detail of the geologic story, plus a look at the Buttes' interior, over on my About.com site. But this is enough background for today's side trip.

Your closest approach to the Buttes on I-5 is at Williams, and that's where you set out for this enchanting feature. Turn off the freeway and head east on state route 20. The road crosses the Central Valley at one of its flattest points. The little town of Colusa sits on the Sacramento River and has a nice park there. This is a worthy side trip—maybe a picnic stop—in itself.

From here there are several different ways to experience the Buttes, depending on your schedule. The shortest trip is a straight drive-by on route 20, after which you can take route 99 north to rejoin I-5 at Red Bluff. Longer versions could include a pass around the little-trafficked north side, a detour into the Buttes on Pass Road, and a complete circumnavigation with optional Pass Road leg. I'll start with the west side.

West Butte Road skirts the ranchlands of the Rampart and several valleys, suitable for orchards and field crops, that penetrate to the Moat. The land of the Buttes is almost entirely in private hands.

Rocks of the Rampart and Castellated Core appear distinct in this view from the north. The lightly travelled road gives many opportunities to stop and admire the landscape. The east side of the Buttes is on the outskirts of Yuba City but otherwise is very similar. There the lower Feather River runs down the valley on its way to join the Sacramento near Knights Landing.

If you get a chance, pull over and inspect the roadside rocks. The Buttes have long been a ready source of stone for lining canals, bolstering levees and making roadbeds. The lava is a beautiful andesite porphyry that is unusually rich in crystals of hornblende and biotite (black) and feldspar (light). Other roadside rocks might include volcanic conglomerates and tuffs dating from the Buttes' fiery youth.

Pass Road takes you inside the Rampart and as close as possible to the Castellated Core. Here South Butte, highest point in the range, rears its head to 2117 feet.

The Maidu tribes thought highly of the Buttes; so do its current landowners. Access for hiking is limited but possible through the Middle Mountain Foundation. Perhaps this side trip will inspire a longer visit to California's nearest thing to Shangri-La.

Recently accelerated erosion in the bed of Cache Creek testifies to a big change upstream: a switch in the drainage of Clear Lake. Photos by Andrew Alden

The rainy, dynamic terrain of the northern Coast Range features many rivers, but very few natural lakes. Any basins that may form by tectonic activity have short lives. Either they fill up with sediment, or rivers erode into them and they drain dry.

Clear Lake, by far the largest lake in the Coast Range, has sediments in it dating back some half a million years. The lake's basin never seems to fill with mud, although Clear Lake has always been shallow. Apparently something builds up the basin's sides whenever the lake outlet threatens to cut downward far enough to drain the lake dry. In recent geologic time, Clear Lake has drained eastward and westward at different times as one exit or the other has been plugged. You can visit both exits and glimpse the geologic evidence yourself.

Today Clear Lake drains east to the Central Valley down Cache Creek through a rugged canyon with high, steep walls. But biologists tell us that the fish of Clear Lake come from both the Russian River and the Central Valley. Without that clue, we might not make much of the straight little valley northwest of Clear Lake, just a few meters above the present lake level. Created by slow faulting, the valley holds some bits of water called Blue Lakes. What could have made Clear Lake drain in this direction?

Clear Lake shows signs of having drained northwest, through Blue Lakes, as well as southeast through Cache Creek, its current outlet.

The east side of Clear Lake is full of young volcanoes ranging in size from Mount Konocti down to a dozen little cones a few tens of thousands of years old. With that in mind it's easy to picture a large lava flow, or the emergence of a small cone, blocking Cache Creek and causing the lake to rise until it spilled through the valley of Blue Lakes to the Russian River.

You can drive up state route 20 from the north side of Clear Lake into this valley, and it's easy to picture it holding a river. Then the road hits a large bump, a hill right in the middle of the valley, and that seems to be the end of the line. But geologic mapping has shown that this is an ancient landslide.

The bare-topped hill blocking the valley past Upper Blue Lake is a landslide. The forested land in front is a younger delta fan.

A look at the topography here is instructive, and Google Maps' "terrain" setting is an excellent way to do that. The photo above was taken from the middle "20" symbol and the hill is marked with an asterisk.

Annotations: V symbols are delta-forming drainages, S marks landslides or possible landslides.

Notice how well-organized the stream drainages are leading down to the lakes. Each of the larger streams has built out a delta of sediment. But west of the lakes is an area of poorly organized, hummocky terrain that closely resembles the body of a landslide. It appears to me that the landslide nearest to Blue Lakes is the smallest and possibly the latest of a whole series.

The native tribes around Clear Lake have old stories of just such a landslide here. If we take them literally, that would place the event within the last few thousand years. The next thing to happen in this scenario is that Clear Lake would rise still further until it overcame the natural dam on Cache Creek and resumed its interrupted eastward drainage. In fact, there's no reason this should have happened only once.

But I mentioned visiting both exits of Clear Lake. Cache Creek goes into roadless country but on the other side, right where it meets state route 16, you can pull over at Cache Creek Regional Park and see this beautiful exposure, about 5 meters high, across the river.

From top to bottom its features are plain as day: a nice flat abandoned floodplain, a layer of coarse river rocks and gravel, the rugged profile of a former streambed, and the tilted bedrock of the Great Valley Sequence. In the typical river, the streambed is cut downward so slowly, only in the largest "hundred-year" storm events, that an exposure like this is never seen. But today's newly invigorated Cache Creek has cut through all this in one clean chop in just a few millennia.

The Lost Hills oil field owes much of its production today to hydraulic fracturing. Photos by Andrew Alden

"Fracking," the ugly nickname for a common oilfield practice, is a rising concern in many places. What about California? Appropriately for a high-tech state, all kinds of advances in underground techniques have been used here. How safe are they? Hard to say.

Working with underground spaces means entering a dynamic environment. California oilfield operators learned that very early in ways that would horrify us today. A century ago, drillers would sometimes tap a highly overpressured oil pool and cause a gusher. The worst of these was the Lakeview gusher, a blowout that began in the spring of 1910 between Taft and Maricopa and lasted more than a year. (The scene today is marked by a plaque.) It ruined the California oil industry for a while—not because of environmental degradation or public revulsion or a government crackdown, but because the flood of oil made the price of crude collapse. Let me put it this way: the problems we have today from oilwell technologies aren't like they used to be.

Site of the Lakeview gusher north of Maricopa. A hundred years later, the ground is still paved with asphalt.

Fracking (hydraulic fracturing) is a way to open up deep rocks by pumping liquids down a borehole at high pressure. The idea is to make a lot of little cracks in tight rocks so the trapped oil can flow out. In the old days, well operators in the Los Angeles basin would goose a fading well by pumping down the crude oil already in the borehole. Today fracking involves water mixed with a little sand, which washes into the new cracks and jams them open. It's widely performed in California to keep old oilfields producing.

You have to pump the fracking water back out before you can extract the oil. Most of the time you can pump it down somewhere else to backfill the space that used to hold the oil, a technique called water injection. The industry learned that about 50 years ago when sinking ground caused shallow earthquakes. The huge Wilmington oil field under Long Beach had six damaging earthquakes between 1947 and 1961 before water injection made them stop.

Today oilfield earthquakes are not a problem in California. Disposal of excess fracking water is our dirty secret. Fracking water gets tainted from its exposure to the oil and natural brines down there, plus it's also mixed with various ingredients to help with the downhole chemistry. Water injection takes care of a lot of dirty fracking water, but the rest needs to be dealt with somehow. In the old days it was dumped on the ground or poured into ponds to evaporate, without much care. Today . . . well, nobody has been keeping track of the industry.

The state government's Division of Oil, Gas and Geothermal Resources (DOGGR) claims to be regulating fracking, but when the state Senate Committee on Natural Resources and Water inquired early last year, the agency had no data to supply. This was a year after DOGGR had gotten extra money, money it had asked for, to develop fracking regulations. The agency now says on its website that it "only has limited information about the use of the practice."

The Environmental Working Group recently compiled what it could find on California fracking and DOGGR's role in overseeing it and issued a critical report called "California Regulators: See No Fracking, Speak No Fracking." The title makes its message clear, and even though I am allergic to activist overstatement of all kinds, I found its factual contents worth heeding. Now the state legislature is considering several bills to encourage more disclosure of fracking; one of them, SB 1054, would require neighboring property owners to be notified of fracking 30 days in advance. The issue is alive, and the legislative sumo match is underway. But the people's watchdog is sitting it out, leaving the fray to lawmakers and lobbyists.

Cattle range in the Big Blue Hills just a few miles from the Harris Ranch feedlot. Photos by Andrew Alden

Driving Interstate 5 through the Central Valley, I find something to like on every mile except one: the smelly vicinity of the Harris Ranch feedlot north of Coalinga. This is how you can avoid it and enjoy some geology for an hour or so.

Assuming you're heading south, the key is to get off of I-5 about 10 miles before the feedlot, at the Route 33 North/Derrick Avenue exit. Think of Derrick as old Route 33, because 33 actually joins I-5 here for a few miles before exiting to the right and meeting Derrick again farther south. See if that makes sense on the geologic map below. This side trip follows 33 into Coalinga and then straight east to the interstate, crossing some interesting structure and a couple of oil fields.

Significant map units from oldest to youngest: Ku, upper Cretaceous marine rocks; Ep, Paleocene marine rocks; E, Eocene marine rocks; M and Mc, Miocene rocks; P; Pliocene rocks; QPc, Pliocene-Pleistocene nonmarine rocks; Q, modern and recent sediment; Qoa, Quaternary river terraces. Magenta lines mark structural arches and troughs, with arrows indicating dips of adjoining strata and plunge of the feature's axis

Derrick Avenue runs for a while through orchard lands parallel to I-5, crossing it twice. Hang in there: it eventually veers away into the Big Blue Hills, as these foothills of the Coast Range are called, out of earshot of the big freeway and smellshot of the big feedlot.

The country here is rolling semidesert, marginal rangeland. The ground underfoot was muddly seafloor for many millions of years, until quite recently in geologic time, around 5 million years ago. Then slow compression across the San Andreas fault raised the Coast Range, buckling these sediments into arching folds. The upward-buckling folds are called anticlines, scientific Latin that means "sloping apart." (Downward-warping troughs, like the one running the length of the Central Valley's western edge, are called synclines.)

Erosion then got to work on the anticlines, peeling away their youngest layers and exposing progressively older rocks. Meanwhile underground, oil and gas worked their way uphill in the newly tilted strata to collect along the center of the nearest anticline. The area around Coalinga, including this part of the Big Blue Hills, is the northern edge of the California oil patch. Now maybe Derrick Avenue's name makes more sense.

Derrick Avenue meets Route 33 again, and you'll turn right on it—going left takes you straight to the stinky feedlot. The road then crosses Anticline Ridge and the heart of the Coalinga Oil Field. Take the Shell Road turnoff if you like where Route 198 comes in; both ways lead to town.

Wells of the Coalinga Oil Field. Photo courtesy Wikimedia Commons

The Coalinga field is the largest of several around here. It was the first great oil district in the Central Valley and remains productive today using enhanced recovery techniques.

Courtesy California Division of Oil, Gas & Geothermal Resources

The oil-bearing hills give way to Pleasant Valley, a syncline filled with young sediment that's occupied by farmland, a state prison, and the town of Coalinga. There are places in town to take a break and find a snack, not to mention the local attraction the R. C. Baker Memorial Museum. Then follow Route 33 out of town again.

It's possible to make Coalinga the start of an extended trip through the oil patch—just follow Route 33 south where it turns right. But to end this side trip, stay on the straightaway, crossing the anticline one last time in the low Guijarral Hills and its moribund oil field to reach the freeway, which is already in progress.

Wikipedia calls this the last working pump in the Guijarral Hills Oil Field. Wikimedia Commons photo

Also still in progress is the rise of the Coast Range. On the afternoon of 2 May 1983, Anticline Ridge jolted up another foot or so in a magnitude 6.4 earthquake. I was sitting in Menlo Park at the time and remember well its ominous slow roll, the sign of a big one somewhere far away.

The nearest place to see California's oldest rock is around Mount Pinos, near Frazier Park west of the Grapevine on I-5. But you can touch a piece of the oldest rock on the whole planet much closer to the Bay Area. Photos by Andrew Alden

I'm glad to see that Ben Burress, my colleague at KQED QUEST, was open to the thrill of deep time as he laid hands on some of California's oldest rock in Death Valley.

When I went to geology school, back in the ice ages, I brought with me the same normal, healthy fascination with extreme age—geological age. At that time there was still a great deal of mystery about the earliest times. To me, the most mysterious thing you could call a rock was "Precambrian," that is, rock dating from the time before the earliest hard fossils appeared, marking the base of the Cambrian Period. Precambrian time amounts to four billion years, nine-tenths of all Earth history. Unlike familiar, fossil-studded post-Precambrian time (I know that's a weird term: geologists call it the Phanerozoic Eon), the Precambrian was an endless succession of enigmatic, mashed-up rocks. Their story wasn't really a story but a pile of hints and fragments—mountain ranges rising and eroding, continents merging and separating, just one damn thing after (or before?) another in the dimness of deep time.

We have a better picture of the Precambrian now, but really, it's still pretty blurry. If you look at the geologic time scale, you'll see that the Precambrian time divisions are set at arbitrary even numbers of years, not significant geologic events. In California, our oldest rocks all originated around 1700 million years ago in the Paleoproterozoic Era, and they all sit in the corner of the state outlined on this geologic map.

Precambrian rocks are shown as scattered patches of dark brown on this high-level geologic map of California. Click it to see it at 1000 pixels.

The outline marks a segment of the North American continent's ancient foundation—the craton—called Mojavia for the Mojave Desert. It's a pretty young part of the craton, and it's all we've got.

The oldest basement rocks of Mojavia are all highly altered—squeezed and stretched rocks classified as gneiss or schist. And they're still on the move today as plate-tectonic interactions are both stretching western North America apart and, in California, yanking it northward along the San Andreas fault system. Just as Sierran granite (shown in red) has been pulled all the way up to the Bay Area, so has a big chunk of Mojavia making up the San Gabriel Mountains.

The westernmost outlier of those Paleoproterozoic rocks crops out in the San Emigdio Range, which forms the rim of the Central Valley southwest of Bakersfield. The quickest way to see them is to turn west off of Interstate 5 toward Frazier Park, then drive up either Frazier Mountain or Mount Pinos (Cerro Noroeste is also possible if you're ambitious). The gneiss shown at the top of this post is on Mount Pinos. It was turned into gneiss around 1450 million years ago, but the rock originated as something else, probably a sandy mudstone, around 1700 million years ago (source, USGS OF-02-406).

Elsewhere in California, you can repeat Ben Burress's experience in Death Valley by walking up the canyon at Badwater, but a more interesting canyon hike with the same Paleoproterozoic rocks starts about 2 miles north of Badwater. And blogger Garry Hayes describes more Paleoproterozoic rocks in the San Gabriels.

The really old rocks in America are found in Wyoming and the states around Minnesota. They date from the Paleoarchean Era and are more than 3 billion years old. One example can be easily seen in Washington, D.C., in a prominent spot between the White House and the Washington Monument: the twin Haupt Fountains, each one made from a 55-ton slab of Montevideo Gneiss from Minnesota. At the time they were made, this was considered the oldest rock in the country.

The reddish, scrambled-looking Morton Gneiss is a popular stone for buildings and gravestones, and at 3524 million years of age it's considered to be the oldest bedrock in the United States. You could travel to Minnesota to see it (there's even an EarthCache for it west of Minneapolis), but don't bother—you probably have samples right in your own town. David B. Williams, author of Stories in Stone, calls it the country's most beautiful building stone.

Morton Gneiss in the Bank of Montreal building. Photo courtesy Jason Woodhead of Flickr under Creative commons license

But you can go older still. There's a Canadian rock from a spot in Labrador called Nuvvuagituq said to be 4.28 billion years old, but the date is still not settled. Today the Acasta Gneiss, also from northern Canada, is the world's oldest firmly dated rock at 4.03 billion years. You can see that one at Rocklin, just up the road. Go to the campus of Sierra College, on the south side, and locate the excellent Earth History Rock Walk.

There, among the assorted amazing and instructive boulders, is a nice chunk of Acasta Gneiss.

But whenever I want to experience the deepest possible deep time, I reach for a meteorite from my collection and lick it. Nearly every common meteorite is older than Earth itself.

View of the Sierra Nevada over Owens Valley from high in the White Mountains. The glories of the high country can be ruined by the body's reaction to the altitude. Photos by Andrew Alden except where noted.

In the medical news this week was a study showing that altitude sickness can be prevented with ordinary ibuprofen. This is interesting for geologists and anyone else who goes to high places. It was particularly so for me, because I served in that research study.

Altitude sickness—a syndrome formally called acute mountain sickness—affects about a quarter of people who ascend from sea level to elevations above 2500 meters, or 8250 feet. The main symptoms are headache, fatigue, nausea, loss of appetite and trouble sleeping. For most victims it goes away in a day or two, but some cases are severe enough to be disabling, and if untreated the brain may sometimes start swelling inside the skull to the point of death.

The best treatment for acute mountain sickness is to move to a lower elevation until the symptoms stop. But that isn't always possible—bad weather may pin you down, for instance. Some people, like search-and-rescue teams or soldiers, simply must carry on. Others, like ski parties or expeditions, are very reluctant to get off schedule. There are prescription drugs for preventing acute mountain sickness, but they have side effects that can be as severe as the condition they're treating. Plus, they need to be taken a day ahead of time—not good for, say, a fire-fighting crew.

So a team of doctors, most of them at Stanford, designed a double-blinded study to test over-the-counter ibuprofen as a preventative. They sent groups of ordinary folks on a two-day summer exercise in the White Mountains, where Stanford maintains high-altitude research facilities. They sent out a call for volunteers. Sounded good to me. I arranged two more nights on the road and made a nice field trip through eastern California out of it.

The study employed 86 people on four separate weekends in the summer of 2010. My group assembled August 20 in Bishop, at the Owens Valley Laboratory, part of the University of California's White Mountain Research Station, and spent the night there at 1240 m (4100 ft). We got up early the next morning.

After breakfast we took our first doses (ibuprofen or placebo, no one knew which), underwent examinations and filled out questionnaires. Among other things, we had our eyeballs ultrasounded.

Photo courtesy Nic Kanaan, MD

Then we drove into the White Mountains and stopped for lunch at the bristlecone pine forest, where I'd never been before. The big snag on the left might be thousands of years old.

Here, at least, it was clear how the range got its name: large areas of dolomite marble. One idea for why bristlecones reach incredible ages here is simply that only dolomite can resist erosion for that long. I thought it was beautiful stuff.

From here, too, the view east over Nevada was immense; range after parallel range marching off to the horizon. Geologists know this as the Basin and Range province, a zone where the crust has stretched westward to one-and-a-half times its original width. The White Mountains, with their southern sister the Inyo Mountains, are the westernmost and highest of these ranges.

Next we parked at a gate at 3545 m (11,630 ft), took another dose, then hiked almost three miles with our backpacks of clothes and bedding to UC's Barcroft Station at 3800 m (12,470 ft).

Photo courtesy Nic Kanaan, MD

I had never hiked at such an altitude before. Walking on level ground was OK, but whenever the path turned uphill my heart and lungs went into overtime and my legs turned to lead. When I couldn't push any more, though, I could pause for just a minute or two and feel fine again. That was uncanny. When the going was good, being there felt at times like floating in the sky.

We left our packs at Barcroft Station and then made one last steep climb to Mount Barcroft's summit, 3975 m (13040 ft). It felt so good to stop, and the view was fantastic. This is looking due west. . .

This wide area of the Owens Valley is a volcanic tableland made up of thick ashflow deposits of the Bishop Tuff; Chidalgo Canyon slashes across it and Lake Crowley in the Long Valley caldera is visible to its rear, in front of the high Sierra.

. . . and this is White Mountain Peak, to the north.

White Mountain Peak is the highest point in the Basin and Range province and the third-highest point in California at 4344 m (14252 ft).

That evening one of the researchers delivered a thorough lecture on acute mountain sickness and other medical issues of high altitudes. It was a peek into the world of adventurers who braved altitudes twice as high as ours, pushing the limits of human capability.

Most of us experienced some of the symptoms of acute mountain sickness, no matter which pills we had taken. We played pool and socialized until bedtime. That's when I noticed how hard it was to sleep; part of it was physiological and part of it was an inability to tolerate snoring.

But I took advantage of the sleepless night by arising before dawn. That was how I managed to witness a rare green flash as the sun first peeked over the Nevada ranges. After that was all downhill: breakfast, a final dose, and a last round of examinations. Then we were free to go. Some of us had plans to tackle White Mountain Peak; mine were to visit the volcanic wonders of Long Valley, at a much more manageable elevation.

And that was it for me until the first paper from the study came out this week in Annals of Emergency Medicine. Ibuprofen, it turned out, works roughly as well as other medicines but is much cheaper to get and easier to take. It won't stop all the symptoms, but it makes a notable difference and may save you from a very bad time. Remember it the next time you hit the high country.