Surrounding the Huntington Library in San Marino, CA., the Desert Garden was started around 1906. Covering its 12 acres is one of the world's largest collections of cacti and succulents. There are approximately 5,000 different species represented, and they're not just your usual cacti. There's a "Cobweb plant" from the mountains of Europe and a Mexican boojum tree, named for the creature in Lewis Carroll's "The Hunting of the Snark." Winter is a good time to view the flowering aloes.
http://www.huntington.org/