The Hagerman Horse was promoted as a state symbol largely to focus attention on the fossil site. In 1988, the Hagerman Horse became Idaho s state fossil, May 28 was proclaimed Hagerman Horse State Fossil Day, and the fossil site was protected in Hagerman Fossil Beds National Monument. Thousands of years separated some eruptions. Over the centuries, the lava s sharp edges weathered away and soil began to form, allowing plants to grow. The Hagerman fossil beds are sandwiched between two lava flows.
Scientists have a pretty good idea of the age of each lava flow.
The bones in between must be younger than the lava beneath them, but older than the younger lava above them. The earliest horses were tiny creatures with several toes on each foot. As they evolved, their toes gradually diminished in size, until horses stood on just one toe on each foot, encased in a hard hoof. One of the great mysteries of science is why horses became extinct in North America, where they evolved. Before they died out, they spread into Eurasia, where true wild horses still survive.