High Quality Content by WIKIPEDIA articles! The Toronto ravine system is one of the most distinctive features of the geography of Toronto, Ontario, Canada. It is a network of deep ravines that form a large urban forest that runs throughout much of the city. For the most part designated as parkland, the ravines are largely undeveloped. The terrain that the city of Toronto sits on was formed after the end of the last ice age some 12,000 years ago. The glaciers flattened the terrain, and deposited a thick layer of loose sand and soil over the region. Over the millennia, even small rivers and creeks eroded this soil cutting deep ravines through what is today the Toronto region. To the north of Toronto is the 1900-km2 Oak Ridges Moraine.