Can't boot 10.10 from flash drive on Macbook Pro

Can't boot 10.10 from flash drive on Macbook Pro

I can't boot 10.10 from my SanDisk cruzer flash drive on my Macbook Pro. I
made my flash drive from
http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-mac-osx. When
I have the flash drive plugged in, I hold down alt when I restart, but
nothing except Macintosh HD and a Recovery Drive (which isn't the flash
drive) shows up. Any suggestions appreciated. Thanks.