Approaching the Chilean border, Parque Provincial Aconcagua is the site of the province’s most prominent attraction—literally so, as the bulky 6,962-meter Cerro Aconcagua  is the “The Roof of the Americas,” the highest peak on two continents.
Parque Provincial Aconcagua, encompassing 71,000 hectares, lies entirely north of RN 7. The main entry point is Laguna Horcones, four kilometers northwest of Puente del Inka , but there’s also access via Punta de Vacas, 20 kilometers east.
Discussions of Aconcagua rarely mention flora and fauna, partly because the mountain’s sheer size and altitude overwhelm most other considerations, and partly because of the focus on climbing. Another reason is that, in the rain shadow of the Andean crest, the park is one of the most barren parts of the Andes, with only a discontinuous cover of prostrate shrubs and grasses. At the highest altitudes, it is almost pure scree and snow.
That doesn’t mean it lacks wildlife, as the Andean condor soars above the ridges and summits, and lesser birds are also present along the watercourses that descend from its glaciers and snowfields. Mammals like guanacos and red foxes may be conspicuous, along with smaller rodents.
The main information post is at Los Horcones, where the rangers have good information and suggestions as well as supplying trash bags for climbers and trekkers; it’s open 8 a.m.–9 p.m. weekdays, 8 a.m.–8 p.m. Saturday. There are also rangers at Confluencia, Plaza de Mulas, Las Leñas  on the Polish route up the Río de las Vacas, and at Plaza Argentina, the last major base camp along the Polish route.
Both hikers and climbers must have permits; those with hiking permits may not continue beyond the base camps. In Mendoza , for most of the year, get permits from the provincial Dirección de Recursos Naturales Renovables (Avenida de los Plátanos s/n, tel. 0261/425-2090, www.recursosnaturales.mendoza.gov.ar , 8 a.m.–6 p.m. weekdays, 9 a.m.–1 p.m. weekends), just inside the gates of Parque San Martín. In summer only, though, permits are available from the nearby Edificio Cuba, and in winter, hiking permits are available at Los Horcones itself (though climbing permits are not).
In past years, however, permits have been available through the provincial Subsecretaría de Turismo in Mendoza, and this could change again. For the most up-to-date information, check the park’s website (www.aconcagua.mendoza.gov.ar ), in Spanish and very readable English as well. Climbers must present proof of their experience and show their equipment.
Permit prices depend on season and nationality (there is now a differential pricing system for Argentines and resident foreigners and for non-Argentines). Low season runs November 15–30 and February 21–March 15, mid-season is December 1–14 and February 1–20, and high season is December 15–January 31. Outside these seasons, fees are reduced.
Rangers collect a US$5 fee for the short walk to Laguna Horcones, and a US$20 fee for the day hike to Confluencia. For non-Argentines, three-day hiking permits cost US$47 except in high season, when they cost US$55. Seven-day permits (more desirable for their greater flexibility) cost US$68 in low and mid-season, US$105 in high season; climbers pay US$158 in low season, US$316 in mid-season, and US$474 in high season. Argentines and resident foreigners pay around one-third of these prices.
Also, the improved fifth edition of Tim Burford’s Chile and Argentina: The Bradt Trekking Guide (Chalfont St Peter, UK: Bradt Travel Guides, 2001), and the second edition of R. J. Secor’s climbing guide Aconcagua (Seattle: The Mountaineers, 1999) are great resources.