It was possible to ride to the outside of the rumble strips, however the shoulder had rough cracks, (or expansion seams) across it every ten feet or so. These cracks were raised and very rough to ride. Additionally, there was shrubbery growing right alongside the guardrail, and often the branches from the shrubbery were blocking the shoulder, so I either had to swerve out into the traffic lane (crossing the rumble strips) or simply allow the branches to brush against my arm. There was also a large amount of rocks and debris on the shoulder, and finally, the traffic volume was fairly large, making it dangerous to ride out in the traffic lane for much of the time.
This was the situation from Bylas to Peridot, on route 70, and after Peridot the shoulder was good. From Globe to Bylas, much of the shoulder had those expansion seams which made for an annoying ker-plunk, ker-plunk as I rode over them, but this section was nowhere near as bad as the section from Bylas to Peridot.
I don't know what the condition of the San Carlos alternate is like, but if I were rdiing this section again, I would take the alternative and not route 70.
Hope this helps and that you have a great ride.