Where are the Ten Most Incredible Places You've Ever Stood? My Number 7, Gubbio, Italy: Castles, Medieval Town, Roman Arena, Faults, and a Dinosaur Killer

It's not always easy, but travel whenever you can. See as much of the world as possible. I passed on both New Zealand and Hawaii three decades ago for reasons that seem trivial today. I didn't go overseas until 2001, but my life since then has been enriched in ways that I can barely comprehend. Few of us have resources enough to just leave and go somewhere, but there are sometimes cheap alternatives...like a geology field class! Yes, you have to work and stuff, but you will see wonderful things, and you'll be traveling with interesting people.

Number seven on my list of most incredible places is Gubbio, in the Umbrian Province of Italy, between Rome and Florence. What's not to like about Gubbio? It has castles, monasteries, medieval fortresses, Roman arenas, plus active faults and beautiful mountains (the Apennines). Plus one of the most significant geologic outcrops in the world (more on that a moment).

Back in 2007, we conducted a joint anthropology/geology field studies journey through Italy and Switzerland. I had never been to Italy before, so I had a lot of book learning to accomplish before I could lead students in mastering of the geology of the country. And because I had never been there, we had a tour company make the logistical arrangements. They had a canned tour which visited all the famous sites (the Colosseum! the Leaning Tower of Pisa!) and it was sometimes a bit tricky to see some of the important geology (although Pompei was a stunning exception; the trip included a hike to the summit of Vesuvius as well as a tour of the ruins). On the day that we drove from Rome to Florence, there was a scheduled visit to the Basilica of St. Francis of Assisi. 

I suppose that some people would have preferred to see the church, but we had noticed that it wouldn't be much of a diversion off our route to see Gubbio instead. It lies east of the main highway high in the Apennines Mountains, the nearly thousand kilometer range that runs down the boot length of the Italian peninsula. The mountains have risen in response to compressive forces related to a convergent boundary in the Mediterranean Sea. In the vicinity of Gubbio, late Mesozoic and early Cenozoic limestone layers have been lifted high into a mountain ridge. In more recent time, faulting formed the valley containing Gubbio. The downdropped crust is called a graben. The eroded fault scarp above the town is called a triangular facet (much of the town is built on the fault surface; see the top picture). That the faults are still active has been shown in dramatic manner, as several deadly earthquakes have shaken the region in recent decades (one of them severely damaged the Basilica of St. Francis in 1997; the L'Aquila quake in 2009 killed 300 people and resulted in some geologists going to prison).

Gubbio has been a crossroads on the Italian peninsula for thousands of years, and numerous cultures have controlled it at one time or another. Its origin dates back to at least the Bronze Age, and some tablets discovered there contain the most extensive known examples of the Umbrian language. The Romans invaded in the 2nd century BCE, and the Roman theater/arena is the second largest known.

The city became powerful and changed hands often during the Medieval period, being on the main transportation routes of the time, but today it is sort of a backwater town, retaining a great deal of its Medieval heritage, including defensive walls, castles, monasteries and churches. But as interesting as these things were, we were there for something else.

The canyon leading down into the town of Gubbio is called the Bottacioni Gorge, and it cuts deeply into the Cretaceous and Paleogene limestone deposits of the Apennines Mountains. In the late 1970s, the father and son team of Luis and Walter Alvarez were here trying to gain some insight on the rate of extinctions at the end of the Cretaceous period, the mass extinction event that did in the dinosaurs about around two-thirds of the species of life on Earth at the time. They decided to test the marine sediments for concentrations of iridium, an element rare on Earth, but relatively more abundant in meteorites. The values were small, a few parts per trillion, and it was hoped that they might provide data on the rate of sedimentation across the Cretaceous-Paleogene boundary (or the Cretaceous-Tertiary K/T boundary).

They got a big surprise. A clay layer at the boundary exposed in the Bottacioni Gorge spiked at around 3,000 parts per trillion, a huge number. In the years that followed, a similar iridium-enriched clay layer was discovered at numerous sites around the world, and researchers soon suggested that a gigantic asteroid perhaps 6 or 7 miles across hit the planet and ultimate caused the extinction of the dinosaurs and other large creatures.

And here we were, ready to lay our hands on the epic moment recorded in the rock when the way was cleared for mammals to take over terrestrial ecosystems on planet Earth. Except there were a few minor problems. For one, we didn't exactly know precisely where it was. And we didn't know if the spot would be marked or if there would be room to park a bus. And though it seems a minor issue, there were 35 people on the trip, and we didn't know where we were going to eat lunch (as all field trip veterans know, the two most important issues are "where and when do we eat?" and "where is the next bathroom?"). I had figured out that the spot was about 2 kilometers upstream from Gubbio, and that there was some kind of old medieval water canal close by.

So I was on pins and needles watching for the outcrop. The first problem cropped up on the edge of Gubbio. The sign on the road quite clearly said "no buses". Our Italian bus driver solved that problem in fine Italian style by ignoring it and driving right on past. We headed up the gorge, rounded a bend, and there was the canal, but I noted with a sinking heart that we had already passed the outcrop on the narrow road, which was pretty much not appropriate for buses (which is what the sign said, I think...). We drove for an interminable number of kilometers up the canyon (I figured about 80 kilometers, but the reality was probably 10), where the driver found a pullout that might be big enough to turn the bus around in.

Those of you who've seen the Austin Powers chase scene where he has a bit of trouble turning a golf cart around will appreciate what our bus driver did on that mountain road with a narrow pullout and a steep canyon wall. This wasn't a Y-turn. This was a Spiro-graph turn, for those of you who remember that toy. Back and forth for what felt like an hour, but was probably more like five minutes. But it finally happened and we headed back down the canyon.

The outcrop containing the iridium layer was in fact marked with a metal placard and an interpretive sign. We gathered around to have a look.

It was not unexpected I suppose that there would be precious little of the clay layer left at the site. Souvenir hunters have produced a huge cavity in the rock, but still, it was a great moment to lay one's hand on the surface where by most accounts, the dominance of the world by the dinosaurs ended. Medieval stories abound of brave knights sallying forth to slay dragons, but it seems the deed was done some 65 million years before we arrived on the planet.

One could see the drill holes left in the rock by the researchers. It is amazing that such a modest outcrop could contain a few atoms of a substance that could reveal a clue towards solving one of the greatest mysteries of the geologic sciences.

Now about the lunch and bathrooms issue. We had been driving for hours and people were getting hungry and, um, uncomfortable. It turned out that there was a single business in the Bottacioni Gorge, but it happened to be a restaurant, and the owner was quite happy to have a crowd of hungry geologists descend on his establishment. He's been catering to geologists for decades as it turns out, enough so that we were asked to sign the geologists register that was first signed by the Alvarez and his assistants!

And the food? By all accounts, the pasta and mushroom dish was the finest lunch we had on our entire journey. It was delicious! If you ever have the chance to visit the Gubbio locality, plan on eating at the Ristorante Bottacioni.