Not along the tour, but visible to the south east of the tour, Known as the Horse Heaven Hills, the country abutting the highway is a great natural grazing area where roving bands of wild horses once fed on the abundant grass.

As US 97 winds into the Horse Heaven Hills, minor streams are crossed. Vegetation becomes greener and thicker. Long-needled, large-coned pines bristle from the mountain slopes, occasionally rising almost from the shoulders of the highway. Here in ages past, the sequoia, extant only in the redwood region of northern California, throve in a great forest; petrified logs of this tree are found among volcanic ash and lava in the area.

This extensive area of low, rolling hills was named in 1881 by James Gordon Kinney, a Yakima pioneer, because the area offered excellent forage and comparative isolation for the bands of wild horses that once roamed in the region.