What backups are on my mac?
These files are stored in /.MobileBackups/ and /.DocumentRevisions-V100/.

I am very surprised that your backup is so large - my Backups are only 300MB!

According to the Time Machine preference pane, TM will "keep local snapshots as space permits". Do you have a lot of spare disk space?

Since these folders are owned by root, to check the size of these folders you'll need to use sudo, or log in as root user. E.g. the command line commands:

sudo du -hs .DocumentRevisions-V100/
sudo du -hs .MobileBackups/