The Miami Rock Ridge is an oolitic, continuous outcrop of limestone, part of the Miami Formation, which formerly covered a large extent of southernmost South Florida; as part of an ecosystem it formed portions of the Everglades. Rising 7 to 8.6 m above sea level, it ranges from northern Miami-Dade County—the approximate latitude of North Miami Beach—southward to the upper Florida Keys and southwestward into Everglades National Park, creating a karst-dominated landscape. The ridge is of Late Pleistocene origin. A series of tidal channels, dubbed transverse glades, formed within valleys in the ridge and acted as outlets for freshwater from the Everglades, thereby modifying the estuarine environment of Biscayne Bay. One of the few areas above pre-drainage sea level, the Miami Rock Ridge was heavily exploited for agriculture and real estate.