Ok, never one to let a mystery go, here's one to muddy the waters. Having a look at Back to the Brink again there's a reproduction of a Dunphy map from 1966/67 (p240 of my edition) which has a "Syncarpia Camp" label well up the creek.
State library has what looks to be an earlier map (1961) with a clearer label:
https://collection.sl.nsw.gov.au/digital/2ZewyD6AjMAm3I've attached the file, hope people can see it. This one has a very clear arrow pointing a spot near what purports to be Arethusa falls. However... my understanding is that that is not the correct positioning of the falls, which are downstream, where the creek turns north.
Of course Dunphy's maps weren't always entirely accurate. I'd say he missed the boat on this one.
But looks like next time I'll have to attempt getting to the base of Arethusa just to be sure...!
Although looking at pictures from above again, it's hard to imagine there's anywhere terrific for a campsite.
https://www.david-noble.net/BlueMtsWate ... eath2.htmlEdit: in Dot English (Butler)'s account of attempting to ascend Arethusa canyon in 1938 she makes reference to camping "close to the junction of Blue Gum track with the Rodriguez Pass Grand Canyon round tour". The party lost the track creekside as they were going up Govetts and headed up the spur to Carne Walls to then get across to Arethusa falls. They got up the falls but couldn't get up the canyon at a certain point so they returned a second time - she says they camped at "Arethusa Falls camp" (with a bunch of boy scouts!) before trying again. Interesting, no mention of Syncarpia at all, and it's not clear if it's the same place they camped at each time. The first one may even have been closer to junction rock (really only 10-15 minutes downstream). But I wonder if the second was at the base of the falls - seems logical if you were going for a second attempt to get close beforehand.
Not syncarpia but interesting none the less and I'm definitely going to have to check it out