Curiosity investigated a spot called Bardin Bluffs at the Darwin waypoint on sol 394. This MAHLI image, taken of a shadowed spot on the outcrop, shows that Bardin Bluffs is a pebbly sandstone. It is gravel-rich, with a sandy matrix and granule- to pebble-sized clasts that are subrounded to rounded in shape. The way that the grains touch each other indicates they were deposited by water. Grains are lumpy and pock-marked, indicating that they collided with each other as they were being transported.
The description is paraphrased from a talk given by Aileen Yingst to the 2014 Geological Society of America meeting.
This is a MAHLI focus merge product; it was made on the rover's sol 396 from data acquired on sol 394.