In the late 1600’s Jesuit missionary and explorer Father Eusebio Kino established a herd of Spanish Barb horses along with cattle and other livestock at Rancho Dolores, Mexico to supply the expanding settlements of the Pimeria Alta region. Father Kino developed a mission system reaching from Mexico to San Xavier del Bac outside Tucson, AZ three centuries ago. He was known as the "Padre on Horseback" for his extensive riding. Father Kino and his Spanish Barb horses were said to travel 70 miles a day, making many trips from Mexico City to the Pimeria Alta settlements. Known for the attributes of endurance, easy keepers and hardiness these Barbs were instrumental in settling the West.

In the 1870’s, according to family history, Dr. Wilbur, an early homesteader near the town of Arivaca, Arizona, purchased a group of these Mission horses. These became the foundation stock of the Wilbur-Cruce rancher strain of Colonial Spanish Horses. Dr. Wilbur’s granddaughter, Eva Antonia Wilbur-Cruce, preserved this isolated herd through much adversity until she sold her family ranch in 1989 to The Nature Conservancy to be included in the Buenos Aires National Wildlife Refuge. Fortunately, the American Livestock Breeds Conservancy became involved. Blood typing and visual inspection supported the oral history and resulted in the rescue and conservatory distribution of the herd. Today Eva’s "rock horses" as she fondly called them noting their ability to negotiate very difficult, rocky, mountainous country with skill and ease – are preserved by breeders in several western states. ("A Beautiful, Cruel Country" by Eva Wilbur-Cruce, 1987).