The Phillips 66 letter/map from Zodiac does NOT mention Mt Diablo. It does point to Clayton,CA.
In his followup letter, Zodiac mentions ‘The Mt Diablo Code’. Is it possible, the word MT DIABLO is in his map code?
Zodiac mailed the map 6/26/70. Just two days before Z mailed it, this article ran in the Oakland Tribune:
It was not until his follow up letter, that Z gave it away that the cipher concerned Mt Diablo.,and he mentions inches along the radians. He inadvertently links himself quite possibly to this radio club.
Google search Radians & Ham Radio, and look at the load of results.
There is more than one way to lose your life to a killer
http://www.zodiackillersite.com/
http://zodiackillersite.blogspot.com/
https://twitter.com/Morf13ZKS
Some examples:
From a Ham Radio License test-
From the The ARRL Extra Class License Manual for Ham Radio
By H. Ward Silver
There is more than one way to lose your life to a killer
http://www.zodiackillersite.com/
http://zodiackillersite.blogspot.com/
https://twitter.com/Morf13ZKS
The Mt Diablo radio club was prepping for their ‘Field Day’ a couple days before the letter. Below is a reprint of a 1969 news story that Radio Clubs had their ‘field day’ events, that last week of June, I wonder if radio clubs ‘field days’ are always that last week of June? I truly think Z gave us a major clue here, I think he was likely connected to that radio club, or another one in the SF bay area
By the way, the guy in the foreground looks like z 
There is more than one way to lose your life to a killer
http://www.zodiackillersite.com/
http://zodiackillersite.blogspot.com/
https://twitter.com/Morf13ZKS
I have tried a couple times to reach out to SF bay area radio clubs,with not much luck
There is more than one way to lose your life to a killer
http://www.zodiackillersite.com/
http://zodiackillersite.blogspot.com/
https://twitter.com/Morf13ZKS
I have to say that the guy in the foreground does looks very much like Zodiac Morf. Good information and the arrow on Zodiac’s map points towards Clayton, but when you are on top of the Mt Diablo ,the clue he gave points just to the right of Clayton. I checked it out using two other compasses from the people there ,to make sure where north was from the top of that MT. Have you checked with the Mt Diablo Historical society about the radio club ?
This is the Zodiac speaking…
Sandy, I will try and check with the Mt Diablo Historical society
There is more than one way to lose your life to a killer
http://www.zodiackillersite.com/
http://zodiackillersite.blogspot.com/
https://twitter.com/Morf13ZKS
The Zodiac cb came from Scandinavia…
LOL, where else could it have come from? Seems appropriate. 
Mike Rodelli
Author, The Hunt for Zodiac; 3.9 stars on Amazon and
In The Shadow of Mt. Diablo: The Shocking True Identity of the Zodiac Killer, a second edition in print format. 4.3 Amazon stars and great Editorial reviews. Twitter:@mikerodelli
