Within Ecuador's system of protected natural areas, Cayambe-Coca Ecological Reserve is considered to have the greatest diversity of flora and fauna. It is an excellent place for bird-watching, with some 900 species of birds having been recorded here. Cayambe-Coca is a large reserve covering many life zones from the summit of Cayambe at 5790 meters (18,997 feet), down to Amazon rain forest. The reserve includes 81 different lakes, many of them wild and difficult to access.

This trek passes through the northwest of the Cayambe-Coca Reserve, a high area with beautiful glacial valleys, rugged peaks, and mostly undisturbed vegetation. The route goes from Laguna San Marcos north to Laguna Puruhanta, through some truly wild country. Both large lakes are popular fishing spots, with abundant trout, but few people venture far beyond the access points; you are likely to go for days without meeting another party. A shorter loop in the Laguna San Marcos area is also mentioned below.

This high páramo, with beautiful views of snow-capped Cayambe, is among the few places in Ecuador where you can see the Andean Condor. There are also hummingbirds, guans, Red-backed Hawks, and tanagers. Waterfowl include the Andean Duck, Andean Teal, and Andean Gull. This is likewise home to the Spectacled Bear, White-tailed deer, and Mountain Tapir. The vegetation is that of a wet páramo, similar to the Llanganates (see A Living Sponge in Trek 16). There are many highland ferns, mosses, and cushion plants, but also plants found in drier areas such as chuquiraguas and gentians. Along the lake shores and in the Río Pisque valley are rich cloud forests.

A project to provide irrigation for the flower growing valleys of Cayambe and Tabacundo is being built in the Laguna San Marcos area. As a result, the level of the lake might change. At the northern end of the park is a buffer zone with forests administered by local communities, including Nueva América. They are trying to encourage eco-tourism as a form of sustainable economic development. Here too, a waterworks project is under construction to divert water from the Río Palaucu for irrigation in the Pimampiro valley.