Within Specimen Ridge , the Yellowstone Petrified Forest consists of a mixture of fossilized , in place ( '' in situ '' ) buried forests and beds of transported logs and stumps . The rare beds that contain buried forests were buried in place ( '' in situ '' ) by volcanic lahars and braided streams . The concentrations of fossilized upright stumps , flat-lying logs , and logs lying at various angles were transported from the higher slopes of adjacent volcanoes and buried by either volcanic lahars or braided and meandering streams . Notably , the 1980 eruption of Mount St. Helens , and other Quaternary and Holocene eruptions of other Cascade Range volcanoes have created virtually identical beds containing either the buried upright standing trunks of forests , transported logs and upright stumps , or a combination of both . These beds consist of a mixture of lahars and stream deposits . Prehistoric logs and upright trunks that are buried in Late Pleistocene lahar and stream deposits of Mount St. Helens were found to be the initial stages of being naturally petrified by silica
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens
Specimen Ridge