Most of Camas Prairie's wind blown soil rests upon Columbia River lava flows from a series of widespread eruptions that covered older, eroded granite rocks here some 6 to 17 million years ago. Some earlier volcanic extrusions, including Kamiah Buttes, between which this highway passes, rise above those Camas Prairie lavas. Perhaps older than 40 million years, they resemble volcanic rocks from Challis in south central Idaho rather than newer lava from farther west. Geologists still are studying how these buttes are related to similar formations elsewhere in Idaho.