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).
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).
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).
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.
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.
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.