"but where are all the small Opuntias, Dave"
Usually sticking to the legs of my jeans Tony, but those wearing shorts had them sticking to their legs and just knocked them off with a stick.
I did not take many pictures since to me they all seemed to be the same species as we went from Santiago in the south to Botija in the north of Chile. They were quite plentiful in some areas, but in others where the other cacti grew I did not see any. No doubt Roger avoided areas where they grew since he sometimes walked about in shorts and open toed sandals instead of walking boots.
It helps Nick if you go with somebody who knows the localities like Roger who has been to Chile around 14 times. Some like the big Copiapoa's can be obvious from the road, but even with many of these you need to know where to go to find them in the first place. Locality names are often just the nearest place having that name and can be kilometres away from where the actual site is, even if you read Ritter's books etc for the locality.
As to Thelocephala's, as said it was an exceptionally wet year and normally most up north are buried, therefore you really need to know the locations where they should be in order to find them and often if they are all back underground you cannot find them anyway. We went to one site for Thelocephala's and Roger said "they are here somewhere" as he had found them before, but we could not find them this time since no doubt they were all underground again, it not having been so wet there. Flowering time is the best to discover them.
If I had been going without anybody who knew the localities I would have seen only a fraction of those I have illustrated. Roger took us from one site having cacti to another with virtually no duds. If I went on my own again I would not be able to re-find most of the localities anyway, the names are where I was told we were even though many of the names themselves were well known to me as Ritter's localities.
The people in the UK who probably know where most of the Chilean cacti are would be Roger Ferryman, Graham Charles, Brendan Burke and Paul Klaassen and no doubt some on the Continent.
Edit:- I should have added to the list people like Paul Hoxey or Brian Bates who have a good knowledge of where the Chilean plants grow and are the ones to tag along with if you can. However Nick don't let me put you off going without somebody who has been before, even though you are likely to see more plants if you do.
The Chileans are very friendly and as we were walking along the street in Vicuna a pickup truck pulled up and the driver shouted "You English?" we said yes and he said "from London?", evidently London is the only place they know in the UK and when we said we were from England he said "Welcome to Chile" and drove on. How he knew we were English and not Americans I do not know, unless it was we were not wearing Stetson's and actually walking, as I gather Americans don't walk unless they have to.
Another thing you will often notice in the small towns if there is no zebra crossing and you are standing at the side of the road, the cars actually stop and wave you across, you don't get that in the UK.