Opportunity is exploring 'Marathon Valley' on the rim of Endeavour crater, inspecting specific outcrops for evidence of clay minerals.

Previously, the rover used the left-front wheel to scuff a red vein feature to break up and expose its compositional material for further investigation.

On Sol 4379 (May 18, 2016), Opportunity bumped 6 feet (1.75 meters) back towards the scuff to set up for an in-situ (contact) investigation of the scuffed material.

The rover also collected some targeted Panoramic Camera (Pancam) 13-filter images and a Navigation Camera (Navcam) panorama.

On Sol 4381 (May 21, 2016), Opportunity began the contact investigation using the robotic arm to collect a Microscopic Imager (MI) mosaic of the scuff and then place the Alpha Particle X-ray Spectrometer (APXS) on the same.

On the next sol, the rover offset the APXS on the scuff by about 1 centimeter and performed another integration.

Opportunity continued on the next sol with yet another APXS offset placement, more MI mosaics and some more targeted Pancam 13-filter imaging.

As of Sol 4384 (May 24, 2016), the solar array energy production is 636 watt-hours with an atmospheric opacity (Tau) of 0.605 and a solar array dust factor of 0.756.

Total odometry is 26.59 miles (42.79 kilometers), more than a marathon.