Hal, Paul, and Marshall take in the view of the Colorado as it winds its way through the Grand Canyon from east to west (east being in the direction the camera is pointed).  The river is an emerald green from the silt it carries as it churns its way toward California water faucets.  This is in stark contrast to the pure, clear water which feeds into the Colorado from it's many tributaries along the way, Hance Creek being but one example.