coastal plain of the Asir region, southwestern Saudi Arabia. It is the central southern section of the great Tihāmah (coastal plain), running down the west coast of the Arabian Peninsula. It is situated between the mountains of western Saudi Arabia and the Red Sea and is immediately north of Yemen. Approximately 40 miles (64 km) in width, its salty tidal plain is of limited agricultural value, but its relatively well-watered upper slopes have been transformed through irrigation and dry-farming methods into the largest and most productive agricultural area in Saudi Arabia.