So I had installed OS X 10.10 on my 2013 iMac to try it out since my MBP is my main computer anyways. However, my iMac is my media hub with much more files loaded onto its 3TB drive. I got tired of messing with Yosemite and went about downgrading to Mavericks. My plan was to create a new Mavericks partition, move everything over to it, delete the Yosemite partition and bring that free space back to the Mavericks partition. I successfully made the 10.9 partition, installed 10.9, and spent quite a while moving everything back over. Then, I rebooted the iMac into the installer via USB and go to Disk Utility. From there I saw an option to merge my existing, working Mavericks install with the 10.10 partition. I clicked that, and it told me that everything on Mavericks partition would be erased to do this. Since that wasn't what I wanted, I hit cancel...or so I thought. Instead, cancel must have been the highlighted (blue) button and the execute button was the white one (which I assumed was cancel). So since I mistakenly didn't take the time to read the buttons, I hit Erase. As soon as it said "Preparing to erase drive", I shut the iMac off and rebooted it. My Yosemite partition is still there, albeit with no OS because I cleared it a few moments before this within Disk Utility. But now, of course, my Mavericks partition that had all of my files is now unable to be found. I know that since I didn't leave it any time to delete anything (or very little if it had), these files are somewhere. But how do I access them now? I do have my MBP and Thunderbolt cable to help. The iMac is currently in target disk mode, but all I can see is the blank Yosemite partition. Sorry for the long post, just wanted to fully explain the situation. Your help is very much appreciated!