Boyden Cavern is a solutional cave system in the located in California's Giant Sequoia National Monument, along the Kings Canyon Scenic Byway, and just west of Kings Canyon [National Park]]. It is formed in Mesozoic marble (metamorphosed limestone). Regular tours of the cave are given by a licensed guide company from the last Friday in April to mid November. It is a cave with many varieties of natural speleothems, including rare "shield" formations. Boyden Cave or Boyden Cavern is located in the deepest river cut canyon of the United States, the 8,200-foot (2,500 m) deep Kings Canyon.