Recover lost partition

Hello.

I managed to install Yosemite in USB drive and boot from it. I would like to know how can I recover files from missing Mac partition (missing because I cannot access it from Finder but in Disk Utility I can see it as disk0s1 -which, AFIK, should be the EFI partition, but actually is my 290GB partition from a failed Bootcamp installation-. I guess the partition must be intact since it's got the original size I provided in Bootcamp assistent, but how can I access it to recover user files or turning it back to be readable?

Any thoughts?

Thanks in advance.