Great Basin National Park, Nevada

Great Basin National Park offers the wildest elevation gradient in the lower 48, jumping from 6,000-foot sage desert to Nevada's only glacier at 13,063 feet within a 30-mile span. Its Lehman Caves contain shield speleothems spanning 8 feet across—30% larger than the typical cave formation size—and the park's darkness rating of 1 on the Bortle scale outperforms #4 Cuyahoga Valley's light-polluted skies by a factor of 10. With just 90,000 annual visitors, it hosts 70% fewer people than the average US national park, yet its bristlecone pines, aged over 4,000 years, rival Congaree's oldest trees in longevity.