Overview Dimond O is ideally located closest to Yosemite National Park's Big Oak Flat entrance and Hetch Hetchy. It's nestled near the banks of the scenic Middle Fork Toulumne River, where warm summer days can be spent wading and fly fishing in the refreshing waters.Recreation Nearby trails include the Carlon Falls Trail near the Carlon Day Use Area, and Yosemite National Park trails accessible from Hetch Hetchy. The Middle Fork Toulumne River is a popular spot for swimming, wading and rainbow