One of the two largest ‘blind’ arches in Zion National Park, (the other is Red Arch Mountain) the Great Arch is visible from the road on the western side of Zion-Mt. Carmel Tunnel. The tunnel itself is a modern feat of engineering, completed in 1930, and just over a mile long — at the time, the longest tunnel of its kind. The tunnel has six ‘windows’ cut into the sandstone, which provide light, views and ventilation for those within the mountain. Ýview The Great Arch was formed by the effects of water, erosional forces, and gravity on the Navajo Sandstone; this landscape varies drastically from that of the other side of the tunnel. Passing through, one sees sandstone formations (like Checkerboard Mesa), which have been thoroughly eroded into interesting shapes with etched faces.    -210 220 2 84