This is really starting to annoy me - I'm trying to create a bootable El Capitan Install USB drive for a Mac Pro 4,1. I'm trying to create it on a 2009 Mac Mini which is already running El Capitan. I've formatted the drive as GUID, but all the guides I've found for creating a USB bootable drive in El Capitan use the .app file downloaded from the store, which I can't do as I'm already running it on the Mac Mini. I've found a bunch of .dmg files, but haven't managed to boot to any of them yet. Anyone know of a guide on how to create a boot drive in El Capitan using a .dmg file? This all used to be so simple... --- Post Merged, Dec 4, 2016 --- Ha, didn't realise they could be redownloaded through App Store purchases. Although the question still stands for older versions of OSX - every now and again I still need Snow Leopard.