Opportunity is on the west rim of Endeavour Crater next to the "Spirit of St. Louis" crater near the entrance of "Marathon Valley." The rover had been conducting an in-situ (contact) science campaign at the outcrop named "Thermopylae."

On Sol 3991 (April 16, 2015), the robotic arm was used to collect a Microscopic Imager (MI) mosaic and then place the Alpha Particle X-ray Spectrometer (APXS) for a multi-hour integration. A small Navigation Camera (Navcam) mosaic was also collected on that sol.

On the next sol, a new Navcam Dust Devil Watch was sequenced. On Sol 3993 (April 18, 2015), further MI mosaics were collected followed by another APXS placement. For the next sol, the APXS was offset to an adjacent target for another integration.

However, during the preparation for the afternoon UHF relay pass the rover experienced a reset, stopping all sequences. The cause of the reset is unknown and still under investigation. Further, an amnesia event occurred later that night for the wakeup to start Deep Sleep.

The rover was restored to master sequence control on Sol 3996 (April 21, 2015). On Sol 3998 (April 23, 2015), Opportunity drove a little over 26 feet (8 meters) to reach the rim of the Spirit of St. Louis crater.

As of Sol 3998, the solar array energy production was 620 watt-hours with an atmospheric opacity (Tau) of 0.766 and a solar array dust factor of 0.731.

Total odometry is 26.25 miles (42.24 kilometers), more than a marathon.