I agree that you don't really need to add mileage to Angel's Staircase and I like a good 8-9k day once in a while. It is 100% singletrack with quite a bit of tech climbing and if you want a harder day just get after it and climb everything on the bike. If the weather is nice you'll want to linger at the passes and the lakes too. But yeah you can start at foggy dew and add another few k of vert. Since it is late season and it is a moto trail I wouldn't do it before significant fall precip at this point though but if you're coming up from Tahoe you may not mind moon dust.
What do you mean by adventure ride? You want sketchy alpine tech, bushwhacking, hike a bike, etc with amazing scenery (Icicle Ridge, Nason/Rock Mountain)? Or just long days in the mountains but still require high quality singletrack?
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