Thousand Islands – Frontenac Arch is one of four ecoregions of the Mixedwood Plains. The Thousand Islands in the Saint Lawrence River have a distinctive flora and fauna and are a part of the biological corridor. The bedrock is mostly gneiss, granite and marble, more than a billion years old. The Frontenac terrain is the youngest of the Ontario portions of the arch, dated at 1.2 billion years old. These rocks were once part of a large mountain chain of the ancient supercontinent of Rodinia. There is also a meteor crater near Holleford, where the shield meets the limestone plains of southeastern Ontario. The area
North American river otter American riverotters are characteristically small or are a type species found in riparian zones. The few occurrences of mammals found in the North American river otter's diet include: muskrats ("Ondatra zibethicus"); meadow voles ("Microtus pennsylvanicus"); eastern cottontails ("Sylvilagus floridanus"); and snowshoe hares ("Lepus americanus"). Records of North American otters preying upon North American beavers ("Castor canadensis") vary; it has been reported in the southern boreal forest of Manitoba. Trappers in Alberta, Canada commonly assert North American river otters are major predators of North American beavers. A 1994 river otter study reported findings of beaver remains in 27 of 1,191 scats