This is particularly wrongheaded, for the reasons noted by MrDibble and Banquet Bear: there are written treaties that go back well beyond living memory, but that are well known to historians. And, in the case of the United States (as a nation) and its individual states (like California), there are many examples of treaties that were either signed in bad faith in the first place, often with groups of Indians who did not represent the whole tribe, and there are also treaties that were signed and then, when later priorities changed, were simply ignored. Those, at least, could be used as a model to enact some sort of viable reparations program.
I think you dismiss a bit too easily the extent to which historians can (and do) know who was where and when in all of this. While disease killed plenty of Native Americans, it was, in most cases, contemporaneous with the arrival of Europeans, rather than preceding them. There were places where disease had ravaged the local Indian populations before sustained efforts at European settlement (parts of New England, for example), but in much of the continent, Europeans made conscious efforts to push Indians off the land and/or wipe them out. And here in California, that effort was perhaps more pronounced and deliberate and brutal than just about anywhere else in the country. It was, as Ben Madley notes in his outstanding book, little more than genocide, and much of it happened about 150-180 years ago.
I’m not using it as a metaphor either, although I understand that it’s not going to happen. And I appreciate that the South African situation is different. I actually wish, in some ways, that the chain of dispossession and injustice were as recent and as easy to track in the US as it is in South Africa, because that might bring some meaningful reparations. I hope South Africa manages to do it.
I’ve been to New Zealand quite a few times (I was there just a month ago), and my best friend has lived there for over a decade. Things certainly aren’t perfect for the Maori, but I think that New Zealand has dealt with the consequences of its colonial past probably better than most (all?) other nations with similar histories. It’s certainly miles better than Australia, where I grew up.