The route through the South Fork American River Canyon remains vulnerable to mudslides and other storm damage. One particularly bad slide closed the highway east of Riverton for 28 days from January 24 to February 21, 1997, only a week after a similar 17-day closure caused by flooding on January 1. A project to make more permanent repairs and prevent future closures began on July 31, and from September 2 to October 24 the highway was closed during the week to allow for more efficient reconstruction. The state signed the detour, which followed Sly Park Road, Mormon Emigrant Trail (the old ridgetop Carson Route), SR 88, and SR 89 (over Luther Pass), as Alternate U.S. Route 50, a designation not approved by the American Association of State Highway and Transportation Officials, which generally assigns new bannered U.S. Highways. After the work was complete, signs were left along the route.