The county's topography makes a dramatic transition from the lower Sonoran Desert to the south to the heights of the Coconino Plateau to the north, and the Mogollon Rim to the east. The highest point above sea level (MSL) in Yavapai County is Mount Union at an elevation of 7,979 ft (2,432 m) and the lowest is Agua Fria River drainage, now under Lake Pleasant.