Bedrock exposures on the surface of Mars are compositionally dominated by olivine, pyroxene, and feldspar minerals, so are understandably thought to be made up by lava flows. However, recent work by Deanne Rogers of Stony Brook University and her colleagues suggests these bedrock materials may instead be formed through sedimentary, pyroclastic air fall, or impact processes. They studied the thermal inertia, morphology, and crater retention properties of these bedrock plains and found they have higher thermal inertia relative to average martian surfaces, thinner or missing regolith, and poor retention of small impact craters. These are not the characteristics of mechanically strong lava flows, but rather more friable materials – rock types that are more easily broken down and eroded.
Link to article: http://onlinelibrary.wiley.com/doi/10.1002/2018GL077030/full