 The Rainbow Bridge National Monument's namesake was also formed by flowing water which created the largest known natural bridge in the Western Hemisphere with a span of , based on a laser measurement made in 2007.Xianren Bridge, also known as Fairy Bridge, in Guangxi, China is currently the world's largest known natural bridge with a span recorded at by the "Natural Arch and Bridge Society" in October 2010, with a precision of ±.Natural bridges can form from natural limestone caves, where paired sinkholes collapse and a ridge of stone is left standing in between, with the cave passageway connecting from sinkhole to sinkhole.