Why is the Owyhee River geology cool? The geology of the Lower Owyhee River is unique for several reasons. First, the oldest rocks on the Owyhee are around 16 million years old (Ma). This may seem old; however, geologically speaking this is very young. To give some perspective, the youngest rocks in the Grand Canyon are 245 Ma and the oldest are about 1.8 billion years old; the Appalachian Mountains are around 250 Ma; and the Rocky Mountains started growing about 70 Ma. The oldest rocks… Read More