https://www.ktvb.com/article/news/local/riggins-us-95-highway-rockslide-road-closed-boulders-detour/277-b48647cf-7bc5-473d-8612-3c04af6e0660mentions a couple of detours
Old Pollock Road (daytime use) - this a 4 mile road on the other side of the river, local road, most likely gravel or oiled gravel.
French Creek Road - for 4x4. Years ago I drove north from McCall on the Waren Wagon Rd but turned around at the Burgdorf Hot Springs, due to lingering snow and rain. French Creek is a switchback road down to the Salmon (4500 ft drop in 16 miles). I read someplace that this was the way north from Boise before US95 was put through.