.The word "Mustang" comes from the Spanish word, mesteno, meaning "stray or ownerless" horse. This term aptly describes all wild horses in the United States.  They descend from horses brought to the Americas by the Spanish.  Although there are several specific mustang breeds, they are generally maintained in closed environments. The term "American Mustang" refers to those that freely roam the American west. 
   In 1971, the United States Congress recognized Mustangs as “living symbols of the historic and pioneer spirit of the West, which continue to contribute to the diversity of life forms within the Nation and enrich the lives of the American people.” Today, Mustang herds vary in the degree to which they can be traced to original Iberian horses. Some contain a greater genetic mixture of ranch stock and more recent breed releases, others are relatively unchanged from the original Iberian stock, most strongly represented in the most isolated populations.
     Today there are fewer than 25,000 free-roaming mustangs.  More than half of them are in Nevada and there are significant populations in Montana and Oregon.  A few hundred survive in Alberta and British Columbia, Canada.