Centuries of scouring floodwaters washed out the arroyo 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. Visitors fascinated by Agate Bridge worked to preserve it through the establishment of Petrified Forest National Monument in 1906. Conservationists believed this ages old natural bridge needed architectural support and in 1911 erected masonry pillars beneath the log. In 1917 the present concrete span replaced the masonry work. Current National Park Service philosophy allows the natural forces that create unusual feature to be left in its natural state. Eventually the natural forces that created Agate Bridge will cause it to fall with or without its supports.