during the very cold pleistocene climates, all of denali was solidly frozen. in the northern areas of the range, it is very much still frozen due to continued cold temperatures. permanently frozen ground is known as permafrost. in denali, the permafrost is discontinuous, meaning due to difference in vegetation, temperatures, snow cover, hydrology, etc., not all of the ground is solidly frozen. the active layer (the layer that freezes and thaws seasonally) can be from to thick. the permafrost layer below the active layer has been measured to be between deep depending on the location of measurement in the park. a stand of white spruce growing on a lower slope of denali is called the drunken forest because of the oddly leaning trees which seem to look "drunk." this appearance is due to the sliding soil beneath them, due to the permafrost difference and freeze-thaw oscillations that occur due to differences in temperature, vegetation, and hydrology.