The West Fork now utilizes the canyons left by the Yakima and Columbia Rivers .
Around 10,000 years ago , the Missoula Floods further altered the landscape , opening up the Horn Rapids area for the Yakima River to flow through .
The West Fork now utilizes the canyons left by the Yakima River and Columbia Rivers .
Around 10,000 years ago , the Missoula Floods further altered the landscape , opening up the Horn Rapids area for the Yakima River to flow through .