"Nubo-Sindian" refers to the biogeographical region along the coast of the Arabian Peninsula.[5] The ecoregion stretches 2,000 kilometres (1,200 mi), from the Jordan River valley north of the Dead Sea, to just short of the Gulf of Aden in Yemen.[2] It also covers the southern slopes of the mountains in the south of the Sinai Peninsula, and reaches inland in low plains at various places along its length on the Arabian Peninsula. Small extensions to the east reach the Shammar Mountains in central Saudi Arabia. The terrain is sand and gravel on the flats, and granite and sandstone in the mountains.[3] The highest point is in the St. Catherine area of the southern Sinai, at 2,388 metres (7,835 ft).[4] The ecoregion bordering to the east is the Arabian Desert and East Sahero-Arabian xeric shrublands ecoregion.