The Appaloosa is a horse breed known for its preferred leopard-spotted coat color and other distinctive physical characteristics. While there is evidence of leopard-spotted horses dating back to the Paleolithic era in Europe, the Nez Perce people of the American Pacific Northwest developed the American breed. They were once referred to by white settlers as the "Palouse horse", probably because the Palouse River ran through the heart of Nez Perce country. Gradually, the name evolved into "Appaloosa". The Nez Perce people lost most of their horses following the end of the Nez Perce War in 1877 and the breed fell into decline for several decades. However, a small number of dedicated breeders kept the breed alive for several decades until a breed registry was formed in 1938. The Appaloosa was named the official state horse of Idaho in 1975. Today the Appaloosa is one of the most popular breeds in the United States. It is best known as a stock horse used in a number of western riding disciplines, but is also a versatile breed with representatives seen in many other types of equestrian activity. The color pattern of the Appaloosa is of great interest to those who study equine coat color genetics, as both the coat pattern and several other physical characteristics are linked to the the "Lp" or "leopard" gene or gene complex, but the precise inheritance mechanism is not fully understood.