Opportunity is in 'Marathon Valley' on the west rim of Endeavour Crater exploring for phyllosilicate clay minerals.

The rover is operating in persistent RAM mode (not using Flash for data storage). Winter power levels have been constraining some rover activities. The rover is conducting both an in-situ (contact) science investigation of a surface target within the central unit of the valley and a Panoramic Camera (Pancam) panorama survey of the North Wall of the valley.

On Sol 4107 (August 13, 2015), Opportunity used the Rock Abrasion Tool (RAT) to brush a surface target. This was followed by the collection of a Microscopic Imager (MI) mosaic and an Alpha Particle X-ray Spectrometer (APXS) placement on the same.

On Sol 4110 (August 16, 2015), the rover continued with more MI mosaics of the target and an offset placement of the APXS for a multi-hour integration. Further Pancam images of the North Wall were taken.

On Sol 4111 (August 17, 2015), the RAT was used to grind 1 millimeter into the surface rock unit. Documentary MI imagery was taken and the APXS placed again. Some diagnostic readouts of Flash memory Bank 7 were performed.

Additional readouts will be done on subsequent sols. On Sol 4112 (August 18, 2015), a complete MI mosaic was collected of the RAT grind was made along with another APXS placement. Deeper grinding is expected in the coming sols. Other than the Flash, Opportunity is in good health.

As of Sol 4112 (August 18, 2015), the solar array energy production was 416 watt-hours with an atmospheric opacity (Tau) of 0.650 and a solar array dust factor of 0.597.

Total odometry is 26.41 miles (42.51 kilometers), more than a marathon.