Due to its steep fall from the Sierra Nevada to the San Joaquin Valley, the Kaweah River passes through a wide range of climate and vegetation zones in a relatively short distance. Historically, the lower Kaweah flowed into a vast area of seasonally flooded wetlands surrounding Tulare Lake, almost all of which have been diked and drained for agriculture. The Kaweah historically formed a large overflow area east of Visalia known as the "Visalia Swamp" and in areas west of Visalia stream channels were poorly defined, often simply disappearing into the marsh lands during periods of high water. The foothill zone is characterized mostly by grassland and rangeland; California oak woodland occurs along the Kaweah River and its perennial tributaries, although its range has been much reduced since Native American times.