If it is cooler, it may be concrete you are over. Concrete won't hold as much heat and therefore cannot give it up at night. Solar radiation also effects the character of the land it hits. Sunlight dries out the topsoil faster and tends to influence the growth of different types of vegetation on the south facing slope. Less moisture also leads to less complete control of erosion and therefore south facing slopes tend to have more exposed rocks and less grass.
Trees tend to produce thick blankets of insulation to protect their roots.
All of these effects are good for the survivalist. He moves back from the rock to the thick mat of needles covering the ground below the tree. Carefully he removes the sticks and pine cones that might make his sleep less comfortable. Then he lays down on his bed. You are the warmer body .