In reply to Offwidth:
It's possible that , prior to the introduction of bird bans, a couple of major rock falls put people off the Main Quarry.
I don't recall any rockfalls in either Lower Left or Lower Right, though I could be mistaken.
In the sixties and early seventies it wasn't unusual to find four or five teams in the quarries on a weekend; I remember one Sunday when a party arrived having been to Tut Braithwaite's wedding the day before. Two of them got chatting with me and asked what the better routes were and I suggested Jericho Wall, my personal favourite.
Within minutes they were halfway up it, not a rope in sight. I was a bit worried because I remembered a scary moment pulling onto the top's ball-bearing finish the year previously but I needn't have bothered.