I'm surprised no one has written an article about U.S. 60/70. The US Route 60/70 designation appears on a 1958 state highways map and is also designated as "Legislative Route 64". The variant name, "Shaver's Summit" is confirmed by the 1958 map. It's not in the possessive form in the USGS data set. I think the U.S. Board on Geographic Names avoids that form.