In conjunction with the assistance of the original poster in the comments above, here is the final solution:
(defun org-icalendar-open-ics-file (file)
(start-process "org-icalendar-open-ics-file-process" nil "open" "-a" "/Applications/Calendar.app" file))
(add-hook 'org-icalendar-after-save-hook 'org-icalendar-open-ics-file)
There is a command line interface to Google Calendar called gcalcli. You can install it using pip:
pip install gcalcli
In order to import calendar files, gcalcli requires the vobject library to be installed:
pip install vobject
The first time you run gcalcli, it will launch a web browser in order to obtain an oauth token, which it will save in ~/....
Here are the settings I use for diary loaded into org-mode. You need to get urls for the apple calendars you want to show in org.
I found the discussion by Adolfo
Villafiorita very helpful.
You'll also probably want to set up some sort of script to automate checking your calendars for new entries. I think the easiest way to do this is to run a script for ...