Partition boots into wrong partition

I have two partitions created, one called "Yosemite" and the other is my default 10.6.8 partition "Macintosh HD".

I successfully installed Yosemite onto the "Yosemite" partition, but when I try and boot the partition by pressing alt-option at startup, it simply boots me back into my Macintosh HD.

Even after attempting to boot to a USB, it still boots back into Macintosh HD. I tried to change the startup disk in System Preferences, but the only things that show up are "Mac OS X, 10.6.8 on MacAir 13" and "Network Startup".

Any and all help would be MUCH appreciated!