Dubai lies directly within the Arabian Desert. However, the topography of Dubai is significantly different from that of the southern portion of the UAE in that much of Dubai's landscape is highlighted by sandy desert patterns, while gravel deserts dominate much of the southern region of the country. The sand consists mostly of crushed shell and coral and is fine, clean and white. East of the city, the salt-crusted coastal plains, known as "sabkha", give way to a north–south running line of dunes. Farther east, the dunes grow larger and are tinged red with iron oxide.