The mountains follow the coast, extending almost to Tunis. The High Tell, an extension of the Saharan Atlas of Algeria, are more extensive and rugged. The Medjerda River valley separates the mountain chains. The Medjerda, which is the only constant stream in Tunisia, flows into the Gulf of Tunis. Northern Tunisia has a Mediterranean climate.
Summers are hot and dry.
Cork oak and evergreen oak forests cover the wetter and more remote slopes of the Northern Tell Mountains. As a result of widespread deforestation from overgrazing and fuel gathering, as well as sparse rainfall, scrub bushes and grasses are the most common vegetation. In central Tunisia an extensive plateau slopes gradually eastward from the High Tell to the coastal plain. The High Steppes are broad alluvial basins separated by low mountains, and the Low Steppes to the east are a flat, gravel-covered plateau. After heavy rains wadis contain intermittent streams that drain into sebkhas, or salt flats, on the coastal plain, where water evaporates.