Opportunity is within 'Marathon Valley' on the west rim of Endeavour Crater conducting a walk-about in search of clay minerals.

The rover is operating in persistent RAM mode (not using Flash for data storage). On Sol 4133 (Sept. 9, 2015), the rover used the robotic arm to collect a Microscopic Imager (MI) mosaic of a surface target and then place the Alpha Particle X-ray Spectrometer (APXS) on the same. A Navigation Camera (Navcam) panorama was collected on the morning of the next sol.

The APXS integrated on the surface target through the evening of Sol 4135 (Sept. 11, 2015). On Sol 4136 (Sept. 12, 2015), another MI mosaic was collected and the APXS placed on a target offset from the previous.

Both Navcam and Pancam panoramas were collected on the morning of Sol 4138 (Sept. 14, 2015). Also on that sol, the project commanded the rover to switch to using the Flash memory as a 'toe dip' diagnostic test of the state of Flash. With the exception of a benign amnesia event, the Flash functioned normally.

The project then commanded the rover back into RAM-only mode on Sol 4139 (Sept. 15, 2015). A long test of Flash memory is planned for next week. Also on Sol 4139 (Sept. 15, 2015), the rover completed a 13-foot (4-meter) bumped to a new surface target.

As of Sol 4139 (Sept. 15, 2015), the solar array energy production was 345 watt-hours with an atmospheric opacity (Tau) of 0.585 and a solar array dust factor of 0.552.

Total odometry is 26.43 miles (42.53 kilometers), more than a marathon.