The Colca river begins high in the Andes, at Condorama Crucero Alto, drops down to the Pacific in stages, changing its name to Majes and then Camana as it goes. Where it runs between the tiny mountain villages of Chivay to Cabanaconde is a deep canyon known as the Colca Canyon. This canyon is reportedly the deepest in the world, thought to be twice as deep as the Grand Canyon in the USA. Unlike most of the Grand Canyon, portions of the Colca canyon are habitable, with pre-Colombian terraced fields still supporting agriculture and human life.
The river and valley were well-known to the Incas and their predecessors, and the Spaniards laid out townships along the valley, no doubt planning to use Rio Colca valley as the route to Cuzco and other Andean locations. They built churches along the way, notably the one at Coporaque, but for some reason, the towns never grew and the route faded from outside memory.
It wasn't until the early 1930's that the Colca valley was explored again, this time for the American Geographical Society. Adventure and Nature in the Colca Valley tells us "Colca Valley has been known by different names: The Lost Valley of the Incas, The Valley of Wonders, The Valley of Fire and The Territory of the Condor. It has even been called one of the Seven Natural Wonders of the World."
In the 1980's, with the Majes Hydroelectric Project, roads opened the Colca to the outside. One of the attractions to visitors is a glimpse into a way of life that has endured in isolation for centuries.
Access now is usually from Arequipa, the second largest city in Peru and often called the 'Ciudad Blanca' (White City) for the white volcanic ashlar stone used for building.
Colca Canyon can be visited any time of year, but it is most beautiful, and safer, after the rains cease. Live volcanos are nearby, and seismic activity can cause landslides or otherwise make the ground unstable. Volcan Sabancayo is more active than Ampato, which you may recall as the site where the now famous Ice Mummy was found.