The Chagrin River is located in Northeast Ohio. The river has two branches, the Aurora Branch and East Branch. Of three hypotheses as to the origin of the name, the most probable is that it is a corruption of the name of a Frenchman, Sieur de Seguin, who established a trading post on the river ca. 1742. The Chagrin River runs through suburban areas of Greater Cleveland in Cuyahoga, Geauga, and Portage counties, transects two Cleveland Metroparks reservations, and then meanders into nearby Lake County before emptying into Lake Erie. The East Branch begins in Geauga County, flows north then west through Lake County, largely in Kirtland, and Kirtland Hills, In these communities the East Branch transects the Holden Arboretum, before intersecting the main in Willoughby. The Aurora Branch begins in northwest Portage County, flowing northwest through Aurora and portions of Geauga and Cuyahoga Counties, intersecting the main branch west of Chagrin Falls. The Chagrin River was designated as a state scenic river in 1979. Natural history Along its banks and tributaries Berea sandstone, Bedford shale, Cleveland Shale, and Chagrin Shale bedrock, are exposed in layers. The river itself was cut through the Allegheny Plateau as glaciers receded in the area at the end of the Wisconsin glaciation. The lowest visible bedrock is Chagrin shale. Named for the river and easily found in the river valley. Chagrin shale, is blue gray in color, an offshore alluvial, silt shale of the Devonian period. This layer is found below about msl. The next layer is Cleveland shale. This is a black shale that is an important source of local fossils. Cleveland Shale is found in the Chagrin River valley between 800 and msl. Bedford Shale is found above the Cleveland Shale layer. This material marks the uncertain transition between the Devonian and Pennsylvanian periods in the region and is also an important source of local fossils. This layer is found in the ravines that carry tributaries of the Chagrin River. Bedford shale is a sand shale and is characterized by its roughly 90° cleavage pattern. Pieces of Bedford shale can look as if they were cut by human hands and are found up to about msl. Berea sandstone is found from around msl to roughly msl. Berea sandstone, is an important local building material. In the nineteenth century it was quarried from the base of Gildersleeve Mountain (in the East Branch watershed).