These are the Rainy River, the Pigeon River, Lake Superior, the St. Lawrence River from Kingston, Ontario, to the Quebec boundary just east of Cornwall, Ontario.
The same is true on the northern shore of Lake Superior, which cools hot humid air from the south, leading to cooler summer temperatures.
Pelee Island and Middle Island in Lake Erie extend slightly farther.
All are south of 42°N – slightly farther south than the northern border of California.
In contrast, the larger, northern part of Ontario is sparsely populated with cold winters and heavy forestation.
Despite the absence of any mountainous terrain in the province, there are large areas of uplands, particularly within the Canadian Shield which traverses the province from northwest to southeast and also above the Niagara Escarpment which crosses the south.
The Carolinian forest zone covers most of the southwestern region of the province.