NASA / JPL-Caltech / UA / JHUAPL / CRISM map courtesy Valerie Fox and Ray Arvidson
Before & After: Map of Glen Torridon, the clay-bearing unit at the base of Mount Sharp
Superimposed on high-resolution image of the base of Mount Sharp is a map made of data from the Mars Reconnaissance Orbiter CRISM instrument. In blue tints, the map shows the strength of a spectral signal attributed to the presence of smectite, a type of clay mineral that suggests the past presence of liquid water. The area with the smectite signal -- informally named Glen Torridon -- also has a distinct rubbly texture. The yellow line shows Curiosity's path up to sol 2366 (3 April 2019). The white path was the plan for Curiosity's future traverse as of sol 2296.
Valerie Fox explains the map: "The CRISM map shows the relative depth of a spectral absorption at 2290 nanometers that is characteristic of iron-bearing smecite clays (nontronite), derived from an Along-Track Oversampled CRISM observation that allows processing to a resolution of 12 meters per pixel. The depth of the absorption is a function of mineral abundance and grain size, surface textures, and dust and sand cover. The detection of smectite clays in this region (informally called Glen Torridon) compared to the rest of the Murray formation is coincident with the distinct rubbly morphology to the south of Vera Rubin Ridge, suggesting textural controls on the spectral signature we see from orbit.