This reserve is at the center of the Peruvian puna, the high-altitude cross section of the Andes, which, at 3,900 to 4,500 meters (12,792 to 14,760 feet), is one of the highest regions in which humans live. Its boundaries begin about 10 km (6 miles) north of town along the shores of Lago de Junín, which, at 14 km (9 miles) wide and 30 km (19 miles) long, is Peru's second-largest lake after Titicaca. Most visitors arrive via day tours from Tarma, but anyone traveling overland from Huánuco via Cerro de Pasco will pass through the reserve.
Flat, rolling fields cut by clear, shallow streams characterize this cold, wet region between the highest Andes peaks and the eastern rain forest. Only heavy grasses, hearty alpine flowers, and tough, tangled berry bushes survive in this harsh climate, although farmers have cultivated the warmer, lower valleys into an agricultural stretch of orchards and plantations. The mountains are threaded with cave networks long used as natural shelters by
humans, who hunted the llamas, alpacas, and vicuñas that graze on the plains. The dry season is June through September, with the rains pouring in between December and March.
The reserve is also the site of the Santuario Histórico Chacamarca (Chacamarca Historical Sanctuary), an important battle site where local residents triumphed over the Spanish conquistadors in August 1824. A monument marks the victory spot. The sanctuary is within walking distance of Junín, and several trails lead around the lake and across the pampas. Bird fans stop here to spot Andean geese, flamingos, and other wildlife on day trips from Tarma.