-xdev, or, if you find it more readable, -mount.
Note, this is by side-effect that it doesn't descend into directories in /mnt. What -xdev/-mount do is stop "find" from descending into directories on other filesystems. If you have multiple mount points, you could:
# for dir in `df -l | grep / | cut -d'%' -f2`; do find $dir <options> -xdev; done
It'll launch multiple "find" processes, but it'll effectively exclude all remote filesystems.
You also could figure out a way to negate -fstype arg to "find", but I couldn't seem to locate anything on that.