One of the most impressive exhibits of its kind will open publicly this weekend. Dinosaur Hall at the Natural History Museum of Los Angeles County contains fossil exhibits unique in the world, including a 25-foot long Triceratops with a skull weighing more than 900 pounds, and the Tyrannosaurus Rex Growth Series, featuring skeletons of the youngest known baby T-Rex, an adolescent and a young adult. The $135 million make-over required two familiar buildings, constructed in 1913 and 1920.