The east coast consists of a narrow band of lowlands, about fifty kilometers wide, formed from the sedimentation of alluvial soils, and an intermediate zone, composed of steep bluffs alternating with ravines bordering an escarpment of about 500 meters in elevation, which gives access to the central highlands. The coastal region extends roughly from north of Baie d'Antongil, the most prominent feature on the east coast of the island formed by the Masoala Peninsula, to the far south of the island. The coastline is straight, with the exception of the bay, offering less in the way of natural harbors than the west coast. The west coast, composed of sedimentary formations deposited in several layers over time, is more indented than the east coast, especially in the northwest, thus offering a number of fine harbors sheltered from cyclones, such as the harbor at Mahajanga. Deep bays and well-protected harbors have attracted explorers, traders, and pirates from Europe, Africa, and the Middle East since ancient times; thus, the area has served as an important bridge between Madagascar and the outside world. Yet the broad alluvial plains found on the coast between Mahajanga and Toliara, which are believed to have great agricultural potential, are thinly inhabited and remain largely unexploited. The west coast is drier than either the east coast or the central highlands because the trade winds lose their humidity by the time they reach this region. The southwest and the extreme south are semi desert; as little as one-third of a meter of rain falls annually at Toliara. Overall, surface water is most abundant along the east coast and in the far north (with the exception of the area around Cap d'Ambre, which has relatively little surface water). Amounts diminish to the west and south, and the driest regions are in the extreme south.