Apple - Location of the resource files for the spinning wait cursor?

Cursors are rendered using CoreGraphics

The Wait Cursor or what is sometimes affectionately know as the "spinning beachball of death" is rendered in CoreGraphics (Apple's 2D rendering engine). Meaning, they are generated on the fly depending on what your preferences are set to (i.e. cursor size).

The CoreGraphics file is located at /System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/CoreGraphics.framework/Versions/A/CoreGraphics

From my research I was able to find the parameters for the Wait Cursor: $23766C - $23D66C"

As far as working with images stored in CoreGraphics, I can point you to this tutorial: Core Graphics on OS X Tutorial

Static Images of Wait Cursor

There is a directory that has static images of the cursors:

/System/Library/Frameworks/GLUT.framework/Versions/A/Resources

Within that directory you will find a number of TIFF files. The specific file is waitCursor.tiff

Opening the file with preview (open waitCursor.tiff) yields the following graphic (it's quite small):

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How I located the file....

The El Capitan cusors link you provided had broken img src links, so I used the one for Yosemite for reference as they are pretty much the same. The icon you wanted is called the "Wait cursor."

So, using the find command in Terminal, I executed the following:

find /System -iname waitcursor*

The command basically says starting from the /System directory, look for all files with the name "waitCursor" in it regardless of case.

I guessed the format of the name from the file naming conventions in the directory you initially provided. For example, the "Resize Down" cursor was called "resizedown".

Here's the El Capitan spinning beachball from materialup.com