Cotahuasi Canyon near the city of Arequipa in Peru is the deepest canyon in the world. Its maximum depth is 3535 metres in the vicinity of Ninancocha, 335 metres more than the Colca Canyon. The Cotahuasi Canyon is an impressive chasm that the river has eroded between two enormous mountain massifs: the Coropuna (6425 m.s.n.m.) and the Sulimana (6093 m.s.n.m.). One extends from spurs of the snow-covered Sulimana to the confluence with the Ocoña river.
It is formed by the Cotahuasi River, arising at more than 4750 m.s.n.m. in the lake Wansuqucha. It receives the tributaries of the Wayllapaña river in the neighborhood of Pampamarka, to the north, and the Huarcaya near Tumipampa, to the west, and is later joined by the Maran River to form the Ocoña River that ends at the Pacific Ocean.
Cotahuasi is located at the highest Andean point of Arequipa, in the south of Peru : UTM 683,370 & 790,415 East & 8’275,582 & 8’380,125 North. Between 14°40´22" & 15°35´27" south latitude, 72°19´15" & 73°18´08" west longitude.
This province is characterized by its steep relief: incised by rivers and gullies, ranging between 1,000 and 6,093 metres, with 19 ecological zones. As is the case with cultures all over the world, the people of highland Arequipa Province are also changing with the times. Nonetheless, the altitude and remoteness of this region mean that residents have retained many of the practices that are now no longer common in neighboring regions
The only road leading to the canyon goes through Chuquibamba in the Condesuyos province, then Aplao in Castilla Province. It begins on the Panamerican Highway near Arequipa. Four bus companies start daily from the Arequipa bus terminal, between 4 and 6 pm. The bus drive is 10-12 hours long, on a road which is unpaved after Chuquibamba. It also goes quite high, through a 4500m pass between Coropuna and Sulimana.
Protected area 
The Cotahuasi Subbasin is a landscape park set up by a 2005 decree. It covers 1,212,175 acres (76x50 miles). This natural reserve preserves an integrated environment where man and nature are living in close harmony, in a preserved cultural microcosm. The difficult topographic conditions have generated specific landscapes like agricultural terraces.
Organic agriculture includes many plants in the reserve : kiwicha, quinoa, mint, dark maize, llacon, fava, oca, beans, arveja (pea), chulpi maize, anise, tarwi. These products are meant to give priority to food supplies to the province. Therefore very little is produced for export. Food autonomy is reached thanks to ecological techniques, rational use of water, promotion of improved seeds, conservation of biodiversity, strengthening of producer associations, and complementary livestock breeding.
The Cotahuasi landscape reserve is a preserved area where the beauty of nature makes your trip a really pleasant experience. The landscapes are extraordinary, with a large biodiversity including many endemic medicinal plants : muña, retama, tara, coca, jara (malva sylvestris), ruda (ruta graveolens), kiwicha, yareta (azorella compacta).
The landscapes are quite many, from the rivers at the bottom of the canyon to the cold desert areas of the summits. There are 12 different ecosystems in Cotahuasi reserve. There are also a number of Inca and pre-Inca works including the many agricultural terraces still in use today. The region is also rich with culture and traditions, preserved by ancient Andean people : weaving, colonial churches, inca tracks, numerous festivals.
See also 
- La Union province
- Cotahuasi portal
- Huaynacotas village
- Rafting the Cotahuasi: One Woman's Whitewater Adventure - Jess Tuerk
- Rio Cotahuasi - Robert Bart
- Rio Cotahuasi River Write Up - Kurt Casey
- www.aedes.com.pe / Images of plants in the Cotahuasi Subbasin Landscape Reserve (Spanish)