I heard it somewhere, I can't find a cite either. It's not the kind of thing they would ever admit to doing, so I'm not sure it would even really be possible to find a cite.
I don't know when it achieved such stature, but it also had been one of the Big 3 Computer Science graduate schools for quite some time. (I.e., MIT, Stanford, and CMU.)
I recall that my undergraduate advisor thought that I probably wouldn't be able to get into MIT, Stanford, or CMU for grad school, but that I'd have no problem getting into Berkeley. He said staying in would be the problem. They had a reputation at the time for accepting a lot of students and then weeding them out.