Yikes. Carnage in the Basque country. A dozen riders down, a half dozen to hospital. All of the big three DNF.
I saw the news on the PCS ticker then went over to look at the feed.
It looked to me like a decreasing radius turn but not one that would be SUCH a big problem for the bunch. I saw this in a Cyclingnews article; perhaps that contributed, too.
Later, local rider Mikel Bizkarra (Euskatel-Euskadi), who was not taking part in the race, observed on X, formerly Twitter, that “On that road, there are a lot of tree roots under the asphalt, which makes the road very bumpy. It's "easy" to go flying."
There were riders going off the road well in front of the first guy down, so this wasn't all domino theory. One of them was Evenepoel. Someone even hopped over the drainage ditch that later consumed a few riders, including Roglic, and kept going in a maneuver right up there with Armstrong-Beloki.
The break was around 2:50 or 2:30 up at the time. Go back three minutes before the crash and watch for a bit; you'll see a very brief replay clip of someone in the break returning from the forest. I'm pretty sure it's the same spot.