Four amateur cave explorers in Sequoia National Park have discovered a vast cave formed 1 million years ago, a labyrinth that stretches more than 1,000 feet into a mountain and features some of the most beautiful rock formations ever seen. Millions of crystals along its walls shimmer like diamonds. Translucent mineral "curtains" hang from the ceiling. Flowstones that resemble spilled paint dot the floor. A lake that might be 20 feet deep fills one of the cave's five known rooms, and passages leading into darkness suggest there is still much more to see. The discovery has excited geologists and cave explorers nationwide because although caves are discovered with almost mundane regularity — 17 of the 240 caves in Sequoia and Kings Canyon parks have been found since 2003 — it is rare to find one so grand. The cave, named Ursa Minor, has been called one of the most significant finds in a generation.