Natural arch
Puente del Inca is a natural rock bridge formed in the Andes Mountains of Argentina. It is made of travertine, a form of calcium carbonate that precipitates from flowing water. At this site, warmed water is being released from a nearby hot spring and as it flows over the River Las Cuevas, carbonate minerals come out of solution and grow the bridge. The deposit is thick enough that large groups of people have used the natural bridge as a route over the river valley for centuries.
