Hi Gareth. If anyone were to know it would be the Sierra Club
http://www.sierraclub.org/
http://www.sierraclub.org/history/ansel-adams/
You might like to drop them a line. They might, at least, be able to point you in the direction of someone with knowledge of the quote.
Best
Paul
Paul,
Thanks very much for that suggestion. I shall look forward to contacting the Sierra Club. They do look like a knowledgable bunch!
Gareth