The most difficult rivers of North America riddles

Yukon, having 1,979 mil (3,185 km), is just 223 miles shorter than Mississippi. Despite its length, there are only four vehicles-carrying bridges across the river.

The gradient between The Great Lakes is generally very shallow. However, the descent between Erie and Ontario is greater than between any of the others, and includes the spectacular Niagara Falls, 51m high.

Rio Grande is the fourth or fifth longest river system in North America, but it flows through arid and desert regions. The average discharge is just 82 m³/s (St Lawrence: 10100, Yukon: 6200, Colorado: 1200). It is also very variable, occasionally rising to over 10000 m³/s or dropping to 1 m³/s. During portions of 2001 and 2002 the mouth of the Rio Grande was blocked by a sandbar.

Located on the Niagara River, which drains Lake Erie into Lake Ontario, the combined falls form the highest flow rate of any waterfall in the world.

The Missouri River is the longest river in North America. Having 2,341 mi (3,768 km), it is longer than the Mississippi (2,202 mi 3,544 km). When combined with the lower Mississippi River, it forms the world's third longest river system, after the Nile and Amazon.

Colorado River established its course through the canyon at least 17 million years ago. Since then, it exposed about two billion years of the Earth's geological history.