The Mexican gray wolf is highly endangered. It is one of the rarest land mammals in the world. By the 1950s, there were very few wolves left in the wild in the United States. The last known wild Mexican wolf in the United States was killed in 1970. Mexican wolves were listed as an Endangered Species in 1976, which means that they are in danger of extinction, or vanishing from our world forever. About 150 of these wolves live in 31 different zoos in the United States and Mexico. The United States Fish and Wildlife Service has developed a plan to restore about 100 Mexican wolves to the wild in parts of Arizona and New Mexico. Mexican wolves are about 4 feet long, stand around 2 ½ feet high, and weigh 70-90 pounds. It is the smallest in size of the many subspecies of gray wolf. Coloration is usually a mixture of gray, black, and white.