No matter how thin your wallet, every first Tuesday (except in July and August), the 50,000-year-old Simi Valley mastodon can be your date. The Natural History Museum of Los Angeles County’s halls of herpetology, ichthyology and mineralogy are open once a month to broke Angelenos dying to keep tabs on the world’s ancient life. The Dinosaur Hall and “Becoming L.A.” are new and exciting exhibits — the latter a 14,000-square-foot display of the story of Los Angeles in six parts:
