In North America, monarchs migrate both north and south on an annual basis, in a long-distance journey that is fraught with risks. The population east of the Rocky Mountains attempts to migrate to the sanctuaries of the Mariposa Monarca Biosphere Reserve in Mexico and parts of Florida. The western population tries to reach overwintering destinations in various coastal sites in central and southern California. The overwintered population of those east of the Rockies may reach as far north as Texas and Oklahoma during the spring migration. The second, third and fourth generations return to their northern locations in the United States and Canada in the spring. Captive-raised monarchs appear capable of migrating to overwintering sites in Mexico, though they have a much lower migratory success rate than wild monarchs do. See section on captive-rearing below. Monarch overwintering sites have been discovered recently in Arizona. Monarchs from the eastern US generally migrate longer distances than monarchs from the western US.