History and Physical Landscape

The Sahara Desert was once a tropical and populated place to be and then became as dry as it is today since the end of the last ice age. The desert has an enormous amount of sand waves with high humid conditions currently, but the landscape was actually a good place to live 8,000 years ago. People and their tribes lived with rain pools, rivers and green valleys. Today, The Sahara Desert is not big for that.

http://knowledge.allianz.com/climate/impacts/?621/green-sahara-how-climate-change-transformed-the-desert

Climate change was the reason why the Desert today is more made up of sand then having any form of grasslands. The Earth's change in orbit around the sun helped cause this during the past 20,000 years roughly. The Earth's orbit around the sun and climate shifts such as areas becoming warmer and rain being shifted south paved the way of how The Sahara Desert looks today.

The Sahara Desert now takes up 3,500,000 square miles of all of Northern Africa. In comparison think of the distance from Los Angeles to New York City! Below is a conformal map and satellite view courtesy of NASA.

http://www.godsgeography.com/africa/africa1.html

The Sahara desert is made up of numerous of landforms but here are two that take up a huge amount of The Sahara Desert. The first being Ergs in which in other words are "Sand Seas" that constantly shift and are fossilized. They cover 20% of Sahara and can rise up to 1,000 feet in height.

http://www.britannica.com/EBchecked/topic/191273/erg

 Second, are the Plateau Mountains of the Sahara Desert in which look to me more like Intrusive volcanic rock, Crypto volcanic rock to be precise. The Plateaus seem to have more of a form of faulting landform than folding due to the different shapes of rock. The sand and mountains seem to be more apart than connected to form a folding type of land.