Macintosh HD missing after Boot Camp

Hello,

This weekend I used Boot Camp to install Windows 10 on a 66GB partition of my hard drive. During the partitioning process, I received an error message that partitioning could not be completed due to an error. I decided to put off troubleshooting until later and just closed Boot Camp, but next time I restarted my machine it booted automatically into Windows 10, completed setup, and Boot Camp is accessible from within Windows.

Now my problem is that the only portion of my hard drive that seems to be accessible is the Boot Camp partition. It's correctly reading the size of 66GB but when I attempt to restart and hold option I don't get the "Macintosh HD" as a startup disk. After booting into internet recovery, I can see the Boot Camp partition and what seems to be the Recovery partition despite that not appearing as an option in startup.

I'm on a late-2013 iMac running OS X El Capitan. I have no idea what my next step should be now, any advice would be greatly appreciated.