The Nevada state quarter features mustangs.
More than half of all Mustangs in North America are found in Nevada with other significant populations in Montana, Wyoming and Oregon and another 30,000 horses are in holding facilities. In fact, Allegro was originally from an Nevada herd.
Here is an illustration from the BLM site that details population distribution:
Mustangs from a herd in Oregon.
Photos are from the Bureau of Land Management site.
For more information please visit the BLM site on wild horses and burros here: