This protected area in the northern Siskiyou Mountains includes a stunning marble cave. The drapery formations in the domes-shaped pit are nothing short of extraterrestrial. Evidence shows that these caves were probably first inhabited by humans over 8,000 years ago. Before that the caves started their formation around 190 million years ago. You can hike by yourself on the outside trails but you must pay for a guided tour with a ranger to see the interior of the caves.