Sepulcher Formation; Mississippian limestones and dolomites; or Precambrian gneiss. Based on radiometric dates and plant fossils from it, the Lamar River Formation is considered to be of Middle Eocene age. Yellowstone Petrified Forest Within the Specimen Ridge, exposures of the Lamar River Formation is well known for the fossils of upright standing, petrified tree trunks and multiple beds containing buried petrified forests and petrified wood concentrations. The concentrations of silicified wood, upright standing, petrified tree trunks, and associated buried petrified forests of Specimen Ridge and adjacent Amethyst Mountain are collectively known as Yellowstone Petrified Forest. They have been known to science and studied for over 130 years. 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. In regard to these fossil forests and other fossils, collecting of fossils in Yellowstone National Park is illegal. In addition, visitors should stay on marked and maintained trails. See also Erling Dorf Mountains and mountain ranges of Yellowstone National Park References External links Anonymous (nd) Petrified Forest, Yellowstone Photo Collection, Yellowstone National Park, National Park Service, Washington DC. Viney, M (2008) Specimen Ridge, The Virtual Petrified Wood Museum. Ridges of Wyoming Landforms of Yellowstone National Park Landforms of Park County, Wyoming Petrified forests Tourist attractions in Park County, Wyoming Paleontology in Wyoming