La Posa Plain is a broad, mostly level desert plain in western Arizona near the Colorado River, spanning part of La Paz County and lying between several mountain ranges that shape its boundaries. Quartzsite stands on its western side, while the plain extends east of the Colorado River Indian Reservation and borders the Kofa National Wildlife Refuge on the west and northwest. Its southern end reaches a drainage divide between the Castle Dome and Chocolate Mountains, and farther north it is crossed by Bouse Wash before continuing toward the area east of Parker. Though remote, it is crossed by major highways used by many travelers.