The dark patch at top center is a field of dark sand dunes viewed through Hidden Valley, which will be Curiosity’s pathway down off the Zabriskie Plateau as it heads for distant Mount Sharp (two-frame Navcam composite). The light area in the foreground is likely a small impact crater, now filled with wind-blown sand and dust.
NASA description (left frame): This image was taken by Navcam: Left B (NAV_LEFT_B) onboard NASA’s Mars rover Curiosity on Sol 695 (2014-07-21 05:19:14 UTC).
Sol 695 raw images (from all cameras), and Curiosity’s latest location map.