Maybe this is old news but I just discovered it, so sharing with others who may not know!
>> From your Desktop, Press ' command ' + ' shift ' + 'g'
>> This should pop up a ' Go to Folder '
>> Paste this : /System/Library/Frameworks/ScreenSaver.Framework/Versions/A/Resources/Default Collections/
Once you have the folder open, you can copy the images to where you keep your other wallpaper images, upload them to Dropbox, or use them anywhere else you need some fresh desktop wallpaper
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Source / Credit: lifehacker.com
>> From your Desktop, Press ' command ' + ' shift ' + 'g'
>> This should pop up a ' Go to Folder '
>> Paste this : /System/Library/Frameworks/ScreenSaver.Framework/Versions/A/Resources/Default Collections/
Once you have the folder open, you can copy the images to where you keep your other wallpaper images, upload them to Dropbox, or use them anywhere else you need some fresh desktop wallpaper
-----------------------
Source / Credit: lifehacker.com