While designing the Eisenhower Tunnel, controversies erupted over how to build the portions over Vail Pass and Glenwood Canyon. The route of US 6 over Vail Pass has a distinctive V shape. Initially engineers thought they could shorten the route of I-70 by about by tunneling from Gore Creek to South Willow Creek, an alternative known as the Red Buffalo Tunnel. This alternative sparked a nationwide controversy as it would require an easement across federally protected lands, through what is now called the Eagles Nest Wilderness. After the U.S. Secretary of Agriculture refused to grant the easement, the engineers agreed to follow the existing route across Vail Pass. The engineers added infrastructure to accommodate wildlife, and had significant portions of the viaducts constructed offsite and lifted in place to minimize the environmental footprint. The grade over Vail Pass reaches seven percent.