The rad peak at that location
could be because of the massive earthwork cuts into the mountains which were required to build that section of highway.
Radon? Natural deposition of uranium?? or some other radioactive element???
It's also possible, at some time over the years, that a runaway truck spilled it's radioactive load if it wrecked after a brake failure coming down that hill. There have been many, many wrecks at that location.
I have little doubt our government would have neglected to inform the public of such an occurrence.
Gosh, if you don't want to eat your sack lunch at the Pyramid Lookout you could stop at Lebec!

Sry, the Lebec Hotel is loong gone!
rc