This has to do with Calendar.app on Sierra (10.12.6).

In the left sidebar, I can see 6 calendars under "On My Mac." I understand why these calendars are here and I need to keep all of them.

However, when I add a new event to the calendar by double clicking on a day's square, I can click on the box that chooses which calendar should receive the new event. In the popup menu, I see another calendar listed under "On My Mac" that is a (seemingly) random 10-digit number.

I would like to know how to delete this mystery calendar.

I can add events to this calendar, but it never shows up in the lefthand sidebar. I've checked the accounts that pipe into my Calendar.app (Exchange, Google) and don't see this mystery calendar anywhere.

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2 Answers 2


This is bit complicated but the only way I know it.

Open ~/Library/Calendars

Leave it open.

Open Calendar > Preferences and set your weird numbers calendar as default.

Now add New event to it.

Go back to the ~/Library/Calendars and look which files (by date/time has changed. That is the one to delete.

Do not forget to change the Default back to your choosing.


@Buscar웃 pointed me in the right direction. I have upvoted that answer.

Disclaimer: I'm no Calendar.app expert. Please don't follow these directions if you're uncertain of how your calendar events are stored and you don't want to accidentally delete something that's unrecoverable.

Open ~/Library/Calendars in Finder and keep it open.

Look at the list of folders that it contains. There will be a folder for each calendar. These folders are named with a random string at the beginning followed by a dot and an abbreviation that represents the type of service used for that calendar. For example:

  • .caldav
  • .calendar
  • .exchange

In my case, I knew that the mystery calendar would be one of the folders that contains ".calendar" in the directory name. Go in to each one of those folders and look at the contents of its Events directory. You will see a list of .ics files. Selecting one of those .ics files will show you a Finder preview of the file, which actually allowed me to see the name of the event that it represented.

So, go to your calendar, and add an event to the mystery calendar. Name the new event something silly that you know is a unique name for an event. I used "Fizzle".

Now open Terminal (or other) and go to the same directory you have open in Finder:

$ cd ~/Library/Calendar

Use grep to search for the name of the new event.

$ grep -r "Fizzle" ./*

Hopefully you'll get only one result that will show you the full path to the .ics that contains an event named "Fizzle".

Use Finder to locate the top-level directory for that calendar. Delete that directory. You'll also need to delete Calendar's cache files:

  • Calendar Cache
  • Calendar Cache-shm
  • Calendar Cache-wal

Quit and reopen Calendar. The mystery calendar should no longer be available.

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