I came here for the same reason....
my biggest problem is that I don't know what to look for - not just clay, but anything else (horsetail for example looks completely different in the handbook than what I found by chance in the forest...)
This is my map - I can see a few blue and beige 'spots' on it, but I have no idea what they mean... (went to random blue spot on map and found blue flowers...)
Edit: Ofc i found clay 10 minutes after making this post ... maybe that is part of search? .... anyway .... map colors do not differ from surrounding at ...