Onondaga (geological formation)

Onondaga Formation Stratigraphic range: Middle Devonian, ~387 Ma PreЄ Є O S D C P T J K Pg N ↓
Type	Geological formation
Unit of	Eifelian
Sub-units	Seneca, Moorehouse, Nedrow, Edgecliff
Underlies	Marcellus Formation
Overlies	Oriskany sandstone
Lithology
Primary	Limestone
Location
Region	Appalachian Basin of eastern North America
Extent	New York to Maryland
Type section
Named for	Onondaga, NY
Location of the Onondaga limestone outcrop in New York State, USA and Ontario, Canada.

The Onondaga Formation is a group of hard limestones and dolostones of Devonian age that form an important geographic feature in some areas in which it outcrops, in others; especially its Southern Ontario portion, the formation can be less prominent as a local surface feature.

In upstate New York and southern Ontario the sedimentary rocks tend to slope slightly southward, and the Onondaga outcrops in a line that usually forms an escarpment (the steep face of a cuesta), because of its resistance to erosion. The outcrop can be traced from the Hudson River valley westward along the southern rim of the Mohawk River valley, passing just south of Syracuse, and along the northern heads of the major Finger Lakes to Buffalo, New York. From Fort Erie, Ontario it runs to Windsor just north of the Lake Erie shoreline, becoming less prominent as one travels westward. It is not distinct west of Windsor, but begins to become noticeable as a steep hill just northwest of Leamington, as it forms a low ridge/escarpment along much of the Lake Erie shoreline.

In several spots it is breached by geologically young streams and spectacular waterfalls are formed, such as at Chittenango Falls just east of Syracuse, Buttermilk Falls at Le Roy, New York and Indian Falls west of Batavia.