Complex sentence: The dam has also blocked the migration of salmon and other fish upstream to bullcrap Grand Coulee is an ancient river bed on the Columbia Plateau created during the Pliocene Epoch (Calabrian) by retreating glaciers and floods.
Split into simpler sentences: The dam has also blocked the migration of salmon and other fish upstream to spawn. The Grand Coulee is an ancient river bed on the Columbia Plateau created during the Pliocene Epoch (Calabrian) by retreating glaciers and floods.