We investigated the thermal properties of the Isidis basin in order to understand the high values (>450 J m⁻² K⁻¹ s^−1/2) located in the southern region of the basin. Thermal inertia data were compared to a variety of complementary data sets, including radar, visible, and results from mesoscale atmospheric simulations. We considered four mechanisms for creating the high thermal inertia, including (1) the thinning of a dust mantle, (2) the presence of unconsolidated, coarse-grained material, (3) high rock abundance, and (4) a high degree of induration. Induration is the scenario most consistent with the data, although we cannot rule out unconsolidated materials and it is likely that rocks contribute to values of thermal inertia to a lesser degree. We also investigated three mechanisms for controlling the geographical distribution of the high thermal inertia values, including (1) the influence of topography, (2) the role of surface morphology, and (3) present aeolian processes. Topography plays a significant role along the southern boundary of the basin but not within the basin itself. THEMIS data show a complex relationship between the thermal inertia and morphology. The wind patterns modeled by the Mars Regional Atmospheric Modeling System (MRAMS) are not fully consistent with the wind directions implied by streaks in the thermal data but are consistent with a second group of streaks observed in the visible data. This suggests that small-scale (tens of kilometers) streaks observed in the thermal data did not form under present-day, nominal winds.