At the time I got into it (early 70s) it wasn't really called underground, that moniker went more to acts like UFO and trip-ridden bummed-out bands, that mostly didn't turn out to have much of a future (Pink Floyd is another exception, for instance).
You had about four choices: Rock, obscure heady music (now Prog), disco, and pop (although the last two were quite interchangeable from a quality standpoint, I suppose). A lot of people were into both Rock and Obscure, and that's how I got into it too.
The term Prog at the time was very different to what it now. In my recollection it actually meant distancing yourself from the pop ditties of the time as produced by Manfred Mann or the Dave Clark Five, as examples. Deep Purple in Rock was quite often considered the height of Prog for just this reason.
Meanings change over time.
Edited by npjnpj - September 30 2008 at 04:14