Via Scientific American:
One of the world's largest natural stone arches has been discovered in the central highlands of Afghanistan. Wildlife Conservation Society staff were tracking the area for wildlife when they chanced on this natural bridge in late 2010. They measured it in February and found that it's 64 meters wide and more than 18 meters tall.
It now ranks as the 12th largest natural bridge in the world, usurping Outlaw Arch in Utah's Dinosaur Natural Monument. Researchers named the feature Hazarchishma Natural Bridge after a nearby village.
The arch includes rock from the Jurassic period, 200 million to 145 million years ago, and the Eocene epoch, 55 million to 34 million years ago. Ancient water running through the now dry Jawzari Canyon carved out the underside of the bridge.
