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 has been exploring the outcrops in this area.

On her 4,000th day on Mars, Opportunity drove about 16 feet (5 meters) to approach a new outcrop for investigation, called "Lambert Field." A post-drive 360-degree Navigation Camera (Navcam) panorama was collected and the Alpha Particle X-ray Spectrometer (APXS) was used to collect an atmospheric argon measurement.

On Sol 4003 (April 28, 2015), the rover used the robotic arm to collect a Microscopic Imager (MI) mosaic of the new in-situ (contact) target and then placed the APXS on the same for a multi-hour integration. Some Panoramic Camera (Pancam) color imagery was also collected.

Another amnesia event occurred on the evening wake up on Sol 4002 (April 27, 2015). This event, like the others, was benign. Regional dust storms have been kicking up dust into the atmosphere. The atmospheric opacity over the rover's site has increased along with some modest cleaning of the rover's solar arrays.

As of Sol 4003 (April 28, 2015), the solar array energy production was 526 watt-hours with an increased atmospheric opacity (Tau) of 1.395 and a solar array dust factor of 0.830.

Total odometry is 26.25 miles (42.25 kilometers), more than a marathon.