Yes, that's the Centennial Valley stretching from I-15 at Monida (no services closer than Lima, about 20 miles north on I-15) east through Lakeview (no services) past Red Rock Lakes NWR, over Hellroaring Creek (the true headwater source of the Missouri River) to Red Rock Pass (graded gravel--Camry rated) and reaching US 20 at Henry's Lake, ID, around 60 miles from Monida or 45 miles from the road junction north of the Lima Reservoir headwater crossing shown as Lyons Bridge on my Benchmark.
I'd traverse the CV along the South Shore Rd, aka Monida-Lakeview Rd, Red Rock Pass Rd, or just MT-509. It's the main road, runs in most places a few tens of feet above the expansive pancake-flat CV valley floor, and passes through Lakeview where the RRLNWR office/visitor center is located. Lakeview has something of a population in summer what with NWR visitors and a number of students and researchers at several field stations. But no fuel or other services.
And, to the west, west of Lima and Dell is the Big Sheep Creek Backcountry Byway softly calling for another 60 mile gravel road excursion through canyons, huge sagebrush hills, the forested Tendoy Range and southernmost Beaverhead Mountains, popping out on MT 324 not far from Bannack...........
Foy