Understand that canyons are deep valleys created by the flow of water over time with steep slopes on both sides. Some people think they are the same as valleys and geologists say that canyon is a unique kind of valley and is generally known this way more in the United States than other countries of the world. Canyon is taken from a Spanish word whose meaning is tube. Grand Canyon is a very well known site and is frequently visited by a number of tourists. Therefore, it is a kind of valley which is very deep and consists of steep slopes on mountains or cliffs.
In the case of a valley, it is a lowland area between any two mountains. A valley will have gentler slopes in most cases. However, they can also have steeper slopes but that is not common. Also it quite wide with mountains on either side and is defined with heavy vegetation. Furthermore, valley is a deep depression between two mountains or cliffs, and also consists of a river. For instance, popular valleys include Kashmir Valley located in India and Indus Valley in Pakistan.