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.

You know Mount Diablo. But do you know what kind of rock it's made of? Photo by Andrew Alden

If you're like me, one highlight of your Christmas celebration is the consternating quiz that columnist Jon Carroll publishes in the San Francisco Chronicle every year. Acknowledging the greatness as well as the priority of the Carroll quiz, I am humbly pleased to bring a geological version to the pages of KQED Quest Science Blogs. The quiz is centered on the Bay Area, which in addition to its other virtues is a premier destination for Earth scientists.

There are 20 questions, each with one correct answer. Some answers may be found in my posts from this year. Some answers can be found on Google and others cannot, but you're coolest if you don't need to search. There is one big hint on this page.

And now the fine print: No prizes are awarded; answers will be added to this post on Boxing Day; until then please post questions, not answers, in the comments. All right? OK!

1. What is California's state rock: gold, mariposite, quartz, serpentine?

2. How big was the 1906 San Francisco earthquake: 7.8, 8.0, 8.2, 9.0?

3. Which of these places is on the North American plate: Aptos, Bolinas, Colma, Davenport?

4. Which of these places is on the Pacific plate: San Francisco, San Jose, Santa Clara, Santa Cruz?

5. What is the highest magnitude earthquake that the Hayward fault is capable of: 6.7, 7.0, 7.5, 8.0?

6. Mount Tamalpais is primarily what rock type: blueschist, chert, marble, melange?

7. What mineral resource has NOT been produced in the Bay Area: coal, mercury, petroleum, uranium?

8. What fossils are NOT found in the Bay Area: ammonites, dinosaurs, hypsodonts, mammoths?

9. What fault continues north where the Hayward fault ends: Calaveras, Rodgers Creek, San Andreas, Zayante?

10. Mount Hamilton is primarily what rock type: gneiss, granite, graywacke, greenstone?

11. What fault continues north where the Concord fault ends: Flint Hills, Green Valley, Greenville, Maacama?

12. Which Spanish word tells you there was once a lime kiln here: calabaza, calavera, calera, calesitas?

13. The San Gregorio fault occurs onshore in what county?

14. Franciscan rocks are mapped in 14 different entities called what: belts, formations, melanges, terranes?

15. What rock type is at the top of Mount Diablo: basalt, harzburgite, rhyolite, schist?

16. Which entity allows personal fossil collecting: BLM, Caltrans, Coastal Commission, state parks?

17. Which North Bay mountain is an actual (former) volcano: Burdell, Konocti, St. Helena, Tamalpais?

18. Mount St. Helena is primarily what rock type: diatomite, serpentinite, slate, tuff?

19. What kind of ore was mined south of Livermore during World War II: iron, magnesium, uranium, vanadium?

20. Where is the Bay Area's only geyser: Calistoga, The Geysers, Great America Park, Mount Diablo?

And here are the answers:

1. California's state rock is serpentine, better known as serpentinite.

2. The 1906 San Francisco earthquake was magnitude 7.8.

3. Colma is east of the San Andreas fault and therefore on the North American plate.

4. Santa Cruz, conversely, is on the Pacific plate.

5. The Hayward fault is considered capable of a magnitude 7.5 earthquake.

6. Mount Tamalpais is primarily melange, an intimate mixture of metamorphic rocks.

7. To my knowledge, uranium has never been produced in the Bay Area.

8. No dinosaur fossils are known from the Bay Area.

9. The Rodgers Creek fault continues north where the Hayward fault ends.

10. Mount Hamilton is primarily graywacke, a variety of sandstone.

11. The Green Valley fault continues north where the Concord fault ends.

12. "Calera" is the Spanish term for a limekiln, where limestone is roasted into lime. You may now look up the other three words.

13. The San Gregorio fault occurs onshore only in San Mateo County, just missing San Francisco and Santa Cruz counties.

14. Franciscan rocks are mapped in 14 different entities called terranes.

15. The top of Mount Diablo consists mostly of basalt.

16. The Bureau of Land Management allows personal fossil collecting on the public lands it administers.

17. Mount Konocti, overlooking Clear Lake, is a former volcano, although the others contain volcanic rocks.

18. Mount St. Helena is primarily tuff, or volcanic sediments.

19. Magnesium ore, the mineral magnesite, was mined in the ultramafic rocks south of Livermore during World War II.

20. The Bay Area's only geyser is in Calistoga, but it's an artificial one that erupts in a drilled hole.

^{Former volcano Mount Konocti overlooks Clear Lake. Photo courtesy Stephen Nakatami of Flickr under Creative Commons license; all other photos by Andrew Alden.}

The Bay Area has been very familiar with earthquakes for at least 20 million years. Volcanoes might seem more remote, but their traces can be seen in many places. Lava flows and ashfall beds are widespread in our rocks, marking the progress of an ancient volcanic center through the area. And while the nearest active volcanoes are beyond the Sierra Nevada, they're close enough to keep an eye on.

California has three major sources of volcanism and one minor one. The minor one is what we have in the Bay Area, but let me mention the others first.

The classic type of California volcanism arises from subduction. This diagram shows how it looks for northernmost California today, with an oceanic plate traveling beneath North America. Water and sediment on top of the downgoing plate acts like a flux, promoting melting in the overlying plate. That's how volcanoes are produced all around the Pacific "ring of fire," and all of California used to look that way.

_{Cross-section from US Geological Survey Professional Paper 1515}

Today the Cascade Range volcanoes are produced by this mechanism. California members of the Cascades include Mount Lassen, which last erupted in 1917, and Mount Shasta, which may have erupted in the 1700s. South of that, this system was interrupted when the San Andreas fault system formed and began extending northward (now the boundary between the two tectonic regimes is a triple junction at Cape Mendocino). An example of Cascade volcanic deposits crops out south of Ocean Beach near San Francisco, a prominent ash bed in the seacliffs of the Merced Formation. It's known as the Rockland ash and came from an ancestor of Lassen volcano, called Mount Tehama, about 600,000 years ago.

The second major kind of California volcanism is beyond the Sierra, in the Mammoth Lakes area and points south. The last "supervolcano" eruption from that area was about 700,000 years ago, and ash from it (the Bishop Tuff) fell here although I don't know where to point you to it. That volcanism is related to stretching of the crust in the Basin and Range province, which basically includes all of Nevada and surrounding counties.

The third type of volcanism is related to Yellowstone, of all places. The geysers and lava flows of Yellowstone are the current location of an eruptive center that began about 16 million years ago in Oregon and slowly burned its way eastward across Idaho, leaving enormous plains of solid lava behind. Northeastern California has a lot of it. One of the first eruptions in that series came from California, sending a glowing flood of basalt lava our way. It flowed more than 200 kilometers as far as Vacaville, where it's mapped as the Putnam Peak Basalt.

_{Boulders of basalt akin to that in Yellowstone and Idaho lie west of Winters.}

You can inspect this rock at leisure on Route 128 west of Winters, about 2 miles west of Pleasants Valley Road. It's the location given at the top of this post.

OK, on to our own local volcanism. As the San Andreas fault system cut northward through our region, it cut off the preexisting subducting plate like a letter opener slicing across an envelope. The plate continued to descend, leaving behind it a traveling "slab window" that briefly allowed the hot underlying rocks of the Earth's mantle to send up magma. In the Bay Area, slab-window volcanic rocks came in three pulses. The first pulse dates from 11 to 8.5 million years ago. Its lavas have been dismembered by motion along the San Andreas and related faults, and now it occurs east of Hollister (the Quien Sabe Volcanics), in the East Bay Hills (well exposed in Sibley Volcanic Regional Preserve), at Burdell Mountain in Marin County, and the Tolay Volcanics between Petaluma and Santa Rosa.

_{Mineral-filled bubbles in lava beds at Sibley Volcanic Regional Preserve}

The next pulse of slab-window volcanism produced the large Sonoma Volcanics between 8 and 2.5 million years ago. A good place to see these is at the Petrified Forest park west of Calistoga, where whole redwood trunks have been fossilized in the silica-rich ash.

Since then, slab-window volcanism has migrated north to the Clear Lake/Geysers region. Mount Konocti, overlooking the lake, is a recent volcanic construction. The famous hot springs get their heat from this volcanism. And the huge geothermal power complex at The Geysers, based on natural steam heated by underlying magma, supplies electricity to the Bay Area, helping you read this story.

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Quest Educational Resources

 Print Guide - Sibley Volcanic Regional Preserve

 Sibley Volcanic Regional Preserve KML file

 Tips to get the kids in your life out into nature

 Designing an Exploration on Google Maps

Additional Links

• Sibley Volcanic Regional Preserve
• California Volcanoes and Volcanics
• Bay Nature: Voice of the Volcano

Lake Toba is all that is left of the volcano
that nearly wiped out mankind.Last blog I talked about how East Africans are genetically more diverse than Asians. Who are genetically more diverse than Native Americans.

From all of this you might have concluded that people are pretty different from each other. They aren't.

People are surprisingly similar at a genetic level. For example, any two people from anywhere on Earth are more similar than two chimps from the same troop. Why are we all so alike?

One possible explanation is that something in our collective past nearly wiped us all out. And we all come from the few survivors who were left.

A likely candidate for this near annihilation event is the Toba volcanic eruption that happened in Indonesia 75,000 or so years ago. This eruption was huge.

It was equivalent to around 1 billion tons of dynamite and was about 3000 times more powerful than the Mount Saint Helens eruption in 1980. It also may have reduced the average global temperature by 5 degrees Celsius, darkened the world for 5 or 6 years, and plunged the world into a new Ice Age.

As you might imagine, this eruption had dramatic effects on species around the world including our own. Estimates of how many people were left range from around 1000-10,000 breeding pairs. The theory is that we are all so alike because we share these survivors' DNA.

Whether true or not, a bottleneck in our past would not make us unique. Lots of species go through these near death experiences.

Scientists think cheetahs went through one around 10,000 years ago. Cheetahs are all so similar genetically that veterinarians can do skin grafts with "unrelated" cheetahs.

And of course, people have created bottlenecks in species too. For example, in the late 1890's there may have only been 20-100 elephant seals left in the world because of hunting. Now there are at least 150,000 spread across the west coast.

Species are in danger long after they go through a bottleneck. They have a pretty limited gene pool which means they may not be particularly healthy and are in danger of being wiped out by, for example, a single disease. Humans are probably OK in this regard (consider natural resistance to HIV for example) but elephant seals, bison, and cheetahs, and many other species may not be.

Fortunately for us we successfully came through our bottleneck. Hopefully, the animals that we've nearly wiped out will too.

Dr. Barry Starr is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA.