The plain most likely used to be constrictive, but due to destructive forces of the earth, weathering tore it down and erosion carried the rest of it away, causing it to be a flat plain.
Constructive forces are when the Earth's gravity causes to shape a landscape of an area. Like making mountains or a canyon. this can also be caused by deposition, erosion, and weathering, all factors of the earth. While destructive forces is the event of w weathering according causing a Constrictive event to happen.