When there are perfect conditions for producing sand dunes, steady wind in one direction and just enough sand, a barchan sand dune forms.
Barchans have a gentle slope on the wind side and a much steeper slope on the lee side where horns or a notch often forms.
 One picture below shows a definite barchan.
When there are perfect conditions for producing sand dunes, steady wind in one direction and just enough sand, a barchan sand dune forms. Barchans have a gentle slope on the wind side and a much steeper slope on the lee side where horns or a notch often forms.  One picture below shows a definite barchan.
Noachis quadrangle