Centuries of scouring flood waters washed out the arroyo, or gully, beneath this 110-foot petrified log to form Agate Bridge. The stone log, harder than the sandstone around it, resisted erosion and remained suspended as the softer rock beneath it washed away.
Enthusiastic visitors fascinated by Agate Bridge worked to preserve it through the establishment of Petrified Forest National Monument in 1906. Conservationists felt this ages-old natural bridge needed architectural support an din 1911 erected masonry pillars beneath the log. In 1917 the present concrete span replace the masonry work.