Crystal Cave has been managed by the Sequoia Natural History Association since 1982. In 2003, vandals destroyed hundreds of formations in three caves in Sequoia National Park, including a dozen in the entrance way to Crystal Cave, so now you can only visit the Cave with a guided tour. Tickets are not sold at the cave entrance, but can be purchased in person at the Foothills or Lodgpole visitor centers in Sequoia National Park.
See this link for details: Crystal Cave tours.
Sequoia Travel Network 