The accumulated sediments and erosional unconformities in the deposits of Mt. Sharp of Gale Crater record multiple periods of wet and dry cycles similar to the episodic climate aridification and later brief wet periods found across Mars [1]. Early post impact (~3.6 billion), an extended period of lacustrine conditions prevailed, leading to over 300 m of lake sediments exposed at the base of Mt. Sharp [2]. This was followed by eolian sediment accumulation perhaps with fluvial deposition interludes [3]. Accumulation ceased and extensive wind erosion shaped Mt. Sharp to nearly its present topography. This erosional event is recorded as the Siccar Point unconformity, which is preserved under a “mound skirting unit”, which locally has been documented to be the remnants of an extensive, large-scale dune field – the Stimson formation [4]. The Stimson formation and the Siccar Point unconformity are predominantly exposed along the Greenheugh pediment, a planar sloping topographic feature that lies downslope of Gediz Vallis [5]. Overlying the Stimson formation on the Greenheugh pediment is the remnant of a fan deposit [5] that may have advanced into transient deep lakes in Gale crater that postdated Stimson fm. deposition [6]. Investigation of the northern exposure of this pediment revealed that the sediments underlying the Siccar Point unconformity (the Carolyn Shoemaker formation) had undergone extensive diagenetic alteration. Nodular alteration was also noted in the basal sediments of the Stimson. These water-driven alterations led to hypotheses about the source and pathways of water which included the possibility that groundwater (derived from runoff from Mt. Sharp) may have developed in the overlying Stimson on the much less permeable fine-grained underlying lake sediments [7]. Here we report that along a southern exposure of the pediment, 0.9 km upslope from the northern area previously investigated (Tower butte area), a discontinuous thin massive unit lies at the boundary between the distinctive eolian dune bedding of Stimson and the underlying strongly diagenetically altered Carolyn Shoemaker formation. We propose that this unit is a result of soft-sediment deformation, a condition favored by groundwater saturation of this basal unit, and possibly driven by impact events before lithification of the Stimson.