The Navajo Steel Arch Highway Bridges are part of US 89A (at least, the newer one is). This is pretty much the last place to cross the river by motor vehicle until you reach Hoover Dam. That's something like 200 miles. The bridge on the left is the older model that was completes in 1929. The bridge on the right was built to match the old design and meet modern highway codes is much newer and opened in 1994. Interestingly, the 1994 bridge is actually 75 feet longer than the 1929 bridge. Infrared.