US Route 491 is a branch of US Route 191 that begins in Monticello, Utah, and runs east and south to end in Gallup, New Mexico. From the junction with US Route 191 in Monticello, US Route 491 runs east and south to Cortez, Colorado; after that, it proceeds south through Shiprock, New Mexico, to end at Interstate 40 in Gallup. The designation of US Route 491 completely replaces the route formerly known as US Route 666. People kept stealing the signs for US Route 666, so sometime in the mid-2000's, FHWA approved the change to the new number of US Route 491. This route lies a little bit west of Mesa Verde National Park, and a bit east of the Four Corners National Monument.
My photo of US Route 491 is the southbound junction marker on US Route 191 in Monticello. This photo was taken at the end of April 2017 as part of the circle around the Grand Canyon. My visit to this spot also gave me a nice shot of the northern end marker for US Route 491, shown below: