We have used Mars Exploration Rover Opportunity data to investigate the origin and alteration of lithic types along the western rim of Noachian-aged Endeavour crater on Meridiani Planum. Two geologic units are identified along the rim. The Shoemaker formation consists of two types of polymict impact breccia: clast-rich with coarser clasts in upper units; clast-poor with smaller clasts in lower units. Comparison with observations at terrestrial craters show that the lower units represent more distal ejecta from one or more earlier impacts, and the upper units are ejecta from Endeavour crater. Both are mixtures of target rocks of basaltic composition. Subtle compositional differences are caused by differences in post-impact alteration along the crater rim. The lower Shoemaker units and the Matijevic formation represent pre-Endeavour geology, which we equate with the regionally mapped Noachian subdued cratered unit. An alteration style unique to these rocks is formation of Si- and Al-rich vein-like structures crosscutting outcrops, and formation of smectite. Post-Endeavour alteration is dominated by sulfate formation. Rim-crossing fracture zones include regions of alteration that produced Mg-sulfates as a dominant phase, plausibly closely associated in time with the Endeavour impact. Calcium-sulfate vein formation occurred over an extended time period, including pre-Endeavour impact and after the Endeavour rim had been substantially degraded, likely after deposition of the Burns formation that surrounds and embays the rim. Differences in Mg, Ca and Cl concentrations on rock surfaces and interiors indicate mobilization of salts by transient water that has occurred recently and may be ongoing.

The Bagnold linear dune field investigated by Curiosity at Mount Desert Island (MDI) is in Gale crater, north of the ~5.5 km high Aeolis Mons mound. False-color images (RGB, 2.496, 1.802, and 1.235 μm, respectively) generated from Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data show the dune field has a reddish-brown color. A sand sheet located south of the Bagnold dunes, the Sands of Forvie (SoF), is darker and lacks the reddish-brown color. Single scattering albedo (SSA) spectra retrieved at 12 m/pixel using along‑track oversampled CRISM observation FRT00021C92 show a long wavelength (1.7 to 2.5 μm) rise for the MDI dunes. Over the same wavelength interval, SoF is characterized by a broad ~2.2 μm absorption feature, consistent with color differences between the two deposits. Checkerboard unmixing of the SSA image cube isolated spectral endmembers within the MDI and SoF. Nonlinear modeling using Hapke (2012) theory implies finer grain sizes for MDI compared to SoF, with inferred abundances of basaltic glass > feldspar > olivine > pigeonite > augite for MDI, and basaltic glass > feldspar > augite > olivine for SoF. These results are similar for the mean spectra of each region and coincide with Curiosity‑based observations that MDI contains smaller ripples with overall finer grains, while SoF has large megaripples and concentrated coarser grains on the crests. Although these deposits are only located ~2.5 kilometers away from one another, wind and local topographic controls influence their grain size and mineralogy.