On the way to the South: Sand Ripples - Sol 1691 (tri-chromatic version; credits: Lunexit)

Caption NASA:"Each day, Opportunity picks a route through two kinds of Martian terrain -- one hard and smooth, the other soft and sandy. Paving the way are flat-lying rocks formed long ago with help from liquid water. Threatening to bury the Rover's wheels are waves upon waves of sand ripples. Both features fill the region that separates the Mars Rover from Endeavour Crater.

In recent weeks, Opportunity has been putting the pedal to the metal.
Since leaving "Victoria Crater", Opportunity has driven almost a mile. Ahead are more miles of similar terrain and interesting things to see. Scientists expect to encounter younger rocks the farther South the Rover travels. They expect to find small rocks ejected onto the landscape when nearby craters were formed. To reach all these things, the Rover must avoid sand traps as much as possible, making the rippled terrain the road not traveled".