We're going to be working in the Finder, with the two windows we asked you to keep open during the previous steps. Keep this Finder window open, because we'll be making use of it in subsequent steps. Once it's complete, the Flash drive will mount on your desktop and open in a Finder window named OS X Base System.

The restore process will take a bit of time.

If requested, supply your administrative password and click OK.

You'll be asked if you're sure you want to erase the USB flash drive and replace its contents with BaseSystem.dmg.

The next step will completely erase the contents of the USB flash drive (or any other bootable device you dragged to the Destination field).

Drag the USB flash drive from the left-hand pane to the Destination field.

If not, drag the BaseSystem.dmg item from the left-hand pane to the Source field.

In the Restore tab, you should see BaseSystem.dmg listed in the Source field.

Once the file is present in the Disk Utility sidebar, be sure to select BaseSystem.dmg, not InstallESD.dmg, which will also be in the list. If the BaseSystem.dmg item is not present in the Disk Utility sidebar, you can drag it there from the Finder window that appeared when you mounted the InstallESD.dmg file. It may be listed near the bottom, after your Mac's internal and external drives. Select the BaseSystem.dmg item listed in the left-hand pane of the Disk Utility window.Make sure the target USB flash drive is connected to your Mac.Launch Disk Utility, located at /Applications/Utilities.The next step in the creation of a bootable copy of the OS X Yosemite installer is to use Disk Utility's Restore capabilities to create a clone of the OS X Install ESD image you mounted on your desktop. We're going to use this Finder window in subsequent steps, so leave this window open. DS_Store, BaseSystem.chunklist, and BaseSystem.dmg. Now that the files are visible, you can see that the OS X Install ESD image contains three additional files.When you've done that, we can continue.

We need to use Terminal to make the system files visible. In actuality, there's an entire bootable system on the image file that is hidden. You may notice that the mounted image seems to contain only a single folder, named Packages.This will mount the InstallESD image on your Mac's desktop and open a Finder window that displays the contents of the mounted file.

Here you will find the disk image that contains the files we need to create a bootable installer.Right-click the OS X Yosemite file and select Show Package Contents from the pop-up menu.Locate the file named Install OS X Yosemite.Open a Finder window and navigate to /Applications.The first step is to gain access to this image file. Deep within the Install, OS X Yosemite Beta file that you downloaded is a disk image that contains all of the files you need to create your own bootable installer.

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