Which Martian plain did NASA's Opportunity rover land on?

NASA's Opportunity rover landed on Meridiani Planum, a broad plain near Mars's equator. The rover touched down on January 25, 2004, on the opposite side of Mars from its twin, Spirit.

Meridiani Planum was chosen because orbiting spacecraft had detected a strong spectral signature associated with gray hematite, an iron mineral that can form in association with water. Opportunity landed inside Eagle Crater and soon examined layered rocks and soil rich in sulfate minerals, evidence that acidic, salty water had once affected the region.

The plain is not a crater: Eagle Crater was the small impact crater where Opportunity first came to rest within Meridiani Planum. Chryse Planitia and Utopia Planitia are separate Martian regions associated with other missions. Opportunity vastly exceeded its planned 90-sol mission and continued exploring until its final communication in 2018.