A PRIVATE PILOT PURCHASED AN AIRPLANE AND FLEW TWO LEGS TOWARD HOME BEFORE STOPPING FOR THE NIGHT. HE DEPARTED EARLY THE NEXT DAY IN VMC. FOLLOWING AN INTERSTATE HIGHWAY, THE PILOT ENCOUNTERED FOG. HE INITIATED A TURN TO REVERSE COURSE, BUT THE AIRCRAFT STRUCK RISING TERRAIN (HILLSIDE) ABOUT ONE HALF MILE FROM THE HIGHWAY.