21. Oak, blackgum, tulip and yellow birch trees are common in the woods that cover the valley walls . 22. The strata exposed in the valley walls provide an important and easily accessible record of Etna's eruptive history. 23. Across the park from this site there are several shallow caves carved by springs in the valley wall . 24. He took water samples from rivers and from higher up on the valley walls at faults and springs. 25. Landslides are very common along the river bank as cliff-like bedrocks are significantly exposed along the river valley wall . 26. These constitute the valley walls of the Great Valley, which runs generally west to east toward the Schuylkill River. 27. The process of erosion carved away the ancient valley walls leaving the lava flows rising above the surrounding terrains. 28. Within Organ Pipes National Park, the valley walls of Jacksons Creek expose Pleistocene volcanic rocks of the New Volcanic Group. 29. The stream's valley walls and the area surrounding the valley has surficial geology featuring bedrock consisting of sandstone and shale. 30. The scarring caused by the avalanche was increasingly higher above the stream bed on the creek valley walls nearer the reservoir.
