I've been reading the Great Divide book for bicyclists, and have been following several threads on riding it on ADV. Living in eastern Idaho just down the road from the SW Montana, Centennial Valley, Red Rock Pass Road, etc., I've been exploring that area this summer to prepare for a major ride next summer with a group. I have some alternates to the official GDR route that folks are following that are far more scenic and rewarding (though not convenient) than the road along Lima Reservoir. They're worth detours they entail. Blacktail Road goes northwest/southeast to link Centennial Valley and Dillon (on I-15). Also, Centennial Divide Road (No. 100), which runs north-south from Centennial Valley, is another far more scenic road, but a major detour from the official GDR route. But it provides for a spectacular loop up onto the awesome 9,500-foot crest of the Gravelly Range, via Gravelly Range Road (most scenic going south, in my view, but great either way). The Gravelly Range loop consists of roads 347 at the southern end (closed Aprl 1-July 1), through gorgeous Eureka Basin to road 290 (Gravelly Range Road) to Warm Springs Road (163) which connects to Centennial Divide Road (100). There is outstanding camping along Centennial Divide Road and Gravelly Range Road, though the latter, being so high, gets cold. The downside to Blacktail Road is that it doesn't not connect logically with Big Sheep Creek National Back Country Byway; it requires some time on I-15 to make that connection. The Centennial Divide Road/Gravelly Range Road loop would be a detour as well. But these are definitely worth the effort to work them in to any ride that includes Centennial Valley. Benchmark Maps' Montana Road & Recreation Atlas is the best reference for all of this. See pp. 120-121 for details. Also, the official GDR misses a picturesque alternate connector to go from Red Rock Pass Road to North Valley/Blacktail Roads. It is at Brundage Bridge, a funky old span across the Red Rock River east of Lima Reservoir. I have photos of all of these recommendations, if anyone would like to see what I'm referring to. Here is one of Blacktail Road.