Forgotten heavy bands from late 60's to early 70's


Have been a fan of hard rock/metal since high school. Always liked the heavy/physcadelic bands equally to the metal bands I grew up with Ozzy-Maiden and Scorpions ect. Recently on Youtube I discovered some heavy/physcadelic bands I was unaware of. 13th Floor Elevators-Five Day Rain-Probe Direction-The Hook and Vahalla. Are these bands albums worth persuing? Feel free to mention any other band that deserves to be heard. Look forward to your responses.
dayglow

@lordmelton - I do remember Sassafras (did they have a Roger Dean cover?), though I don't think I'd seen or heard them; Beckett is another I recall seeing in the import section. I used to be in the record business in the 70's and would always read the English weeklies. We had a good local FM station then in San Jose that played nothing but prog and psychedelic music; shame it didn't last longer, but they're the ones who turned me on to Man and the whole Welsh scene (and the Canterbury scene as well). In fact one of their DJ's, Ron Sanchez, ended up producing 'Call Down the Moon'. 

Medicine Head, they released their Dark Side of the Moon album just before Floyd and nearly caused Floyd to change the name.

@lordmelton - it might be Greenslade, but Roger did SO many album covers back then, who knows what I was thinking of? 

That Medicine Head one - wow, that's a real obscuro!!