rises above a broad, high plain which stretches to the Hudson River to the east. On the west the low foothills of the Appalachian Mountains mingle with a low flat made by the Rondout Creek and Sandburgh Creek, the Basha Kill and various small kills, as well as the Neversink River and Delaware River at the southern end. These adjacent valleys are underlain by relatively weak sedimentary rock (e.g., sandstone, shale, limestone). Natural environment There is an unusual diversity of vegetation on the ridge, containing species typically found north of this region alongside species typically found to the south or restricted to the Coastal Plain. The results is an area where many regionally rare plants are found at or near the limits of their ranges. Other rare species found in the area are those adapted to the harsh conditions on the ridge. Upland communities include chestnut oak and mixed-oak forest, pine barrens including dwarf pine ridges, hemlock-northern hardwood forest, and cliff and talus slope and cave communities. Wetlands include small lakes and streams, bogs, pitch pine-blueberry peat swamps, an inland Atlantic white cypress swamp, red maple swamps, acidic seeps, calcareous seeps, and a few emergent marshes. Geology The ridge is primarily Shawangunk Conglomerate, a hard, silica-cemented sedimentary conglomerate of white quartz pebbles and sandstone that directly overlies the Martinsburg Formation, a thick sequence of turbidite deposits of dark gray shale and greywacke. The Martinsburg Formation was deposited in a deep ocean basin during the Ordovician (470 million years ago). The Shawangunk Conglomerate was deposited over the Martinsburg Formation in thick braided river deposits during the Silurian (about 420 million years ago); both sequences of sedimentary rock were subsequently deformed in a continental collision associated during the assembly of the Pangean supercontinent during the Permian (about 270 million years ago). This collision deformed strata within the ridge in a northward plunging series of asymmetric folds (e.g., anticlines and synclines) that are inclined gently westward. These same folds, involving strata that overlie the Shawangunk Conglomerate, are exposed north of Shawangunk Ridge in the Rosendale Natural Cement Region, where they can be directly examined in abandoned mines. Strata along the eastern margin of Shawangunk Ridge are truncated by erosion, resulting in the prominent cliffs characteristic of Shawangunk Ridge. The Shawangunk Conglomerate is very hard and resistant to weathering; whereas the underlying shale erodes relatively easily. Thus, the quartz conglomerate forms cliffs and talus