From Bushwalk Australia
A narrow steep-sided valley or canyon, which may have a river or creek flowing through it. A gorge is somteimes formed when a waterfall retreats upstream, and erodes the rock at the base of its valley. Gorges can often be found in limestone karst areas, formed by the collapse of underground cave roofs. Launceston's Cataract Gorge is possibly the most well-known gorge in Tasmania.