The Zion Narrows, part of Zion National Park, is a gorge carved out by the Virgin River, stretching 16 miles long, reaching about 2,000 feet deep and spanning only about 20 to 30 feet wide in some areas. Ranked No. 5 in National Geographic s America s Best 100 Adventures, the Zion Narrows is no easy feat. The river marks the route, so there really isn t a maintained trail, and at least 60% of the hike involves wading and sometimes swimming in the river. Highlights include natural springs, hanging gardens and ponderosa pines.