I note that recent soilT profiles show intense heating of the top soil layers during the day, followed by almost instantaneous cooling back to below freezing. Indeed, there is a "rebound" effect where the top soil cools to below the lower soil, associated with a change of sign in the heat flux. I believe these large changes should indicate a low heat capacity, though the Cv values are just average. I do note that the soil density is lowest at river7, so Cp (mass-weighted) may be quite low.