What are the characteristics of an overwintering sites in Mexico?

Monarchs in Mexico overwinter in high elevation oyamel fir forests in the Transvolcanic mountain range of central Mexico. Typically the locations that they find favorable are about 2 miles above sea level, or about 3,000 meters. These sites are typically found on moderately steep south-soutwest facing slopes and are usually in close proximity to a stream or source of water. The temperature at these locations is fairly cool, typically just a bit above freezing. It can get warmer during nice days, but nights remain fairly cool.