Spectacular landscapes occur on uplifted and deeply dissected sedimentary rocks. Wind and water erosion has left impressive canyons, cliffs, buttes and mesas. Soils of the region are dry generally lacking organic material and distinct soil profiles and are high in calcium carbonate. This aridity is the result of the rain shadow of mountain ranges as they intercept the wet winter air masses brought by the westerly and easterly winds. High mountains also block some moist Gulf Coast air masses that cross the Great Plains.
Large valleys occupy the southernmost region of the North American deserts.
Average annual precipitation ranges from about 130 mm to 380 mm. Some southern areas are dominated by a more episodic summer rainfall pattern, while the northern deserts tend toward a winter moisture regime with some precipitation falling as snow. The ecological region is comprised of a mixture of mountains, hills, tablelands and plains. It occupies an area of tectonic instability at the interface of the North American and Pacific tectonic plates and contains a variety of active faults. The central valley is a broad trough has rivers and is filled with large quantities of silt, sand and gravel washed down from surrounding mountains.