San Diego Natural History Museum in downtown San Diego's Balboa Park — known locally as The Nat — traces its founding to October 9, 1874, making it the oldest scientific institution in Southern California and the second oldest west of the Mississippi. Four floors of galleries and a giant-screen theater occupy a 1933 William Templeton Johnson building that doubled in size with a 90,000-square-foot expansion in 2001, anchoring the east end of El Prado as a scientific counterpart to the botanical stewardship at Japanese Friendship Garden & Museum across the park. A research collection exceeding eight million specimens spans nine departments — from birds and mammals to paleontology, botany, herpetology, and mineralogy — with the Joan and Irwin Jacobs Center for Science and Conservation focusing field work on Southern California and Baja California Peninsula biodiversity. Live-animal exhibits featuring rattlesnakes, iguanas, and a working beehive share gallery space with a Foucault pendulum and fossil installations including regional mastodon and megalodon specimens, bridging the natural-science and cultural-history programming presented at Museum of Us up the promenade. The museum's founding members helped establish both Torrey Pines State Natural Reserve and Anza-Borrego Desert State Park, and current conservation partnerships with the U.S. Fish & Wildlife Service extend that 150-year legacy through binational species monitoring and land-acquisition advisory work across the Southern California-Baja California border region.