Day four has a clear split: irrigated farmland first, desert after that. From Calexico, the route heads north out of the border city, passing straight roads, canals, fields and low settlements in the Imperial Valley. The opening kilometres sit partly below sea level; the terrain is flat, exposed and shaped by the agricultural water network. Toward Holtville and farther northeast, the towns get smaller, fields more often end against dry ground, and the gaps between shade, shops and junctions become longer. Later, the route leaves the valley floor. The road gains elevation slowly, the asphalt runs through bare desert ground, and just before Glamis the Imperial Sand Dunes appear: pale dune fields directly beside the road, clearly different from everything earlier on the stage.
