Reconnaissance geologic map of the Muwassam Quadrangle, sheet 16/42 D, Kingdom of Saudi Arabia

The Muwassam quadrangle, bounded by lat 16°00’ and 16°00’ N. and long 42°30’ and 43°00’ E., includes the very southernmost territory of the Kingdom of Saudi Arabia. The quadrangle is named after Muwassam, a small town and minor border-crossing point for traffic into the Yemen Arab Republic. An asphalted road from the Jizan quadrangle to the north terminates at Muwassam town. Much of the quadrangle includes part of the Yemen Arab Republic and a portion of the Red Sea.

All of the mapped area is occupied by coastal plain bordering the Red Sea. The flat coastal plain is covered by Quaternary surficial deposits overlying a sequence of Tertiary rocks as much as 5 km thick. The coastal plain is separated from the Red Sea by zone of supratidal sabkha deposits, offshore bars, islands, tidal md flats, and shallow lagoons. The sea is shallow, less than 200 m deep, and forms part of the shelf marginal to the main axial trough of the Red Sea.