People talk about what research needs Wikipedia is actually good for. I find it most useful for the books cited on its pages, often treatises I hadn't known on subjects that interest me.
Some are better than others, though. I've been playing around with U.S. historical population statistics, and I've found a number of tables on Wikipedia city entries that cite Population History of Western U.S. Cities and Towns, 1850-1990 by Riley Moffat as a source. Sounds like a book for me, so I ordered it from the library on ILL.
It's terrible. Compiled as a hobby by a reference librarian over 30 years of work, it takes its data from census reports and from estimates in the Rand McNally Commercial Atlas, without any indication of which data comes from which source. It's full of typos in the place names, and probably in the data, too. What really gets me is that Moffat provides no information on the cities. They're just listed alphabetically by name under each state, with no indication of where they are, except that if there's two by the same name, he'll give the counties. He should have given at least county for all of them (this info would have been easily available in his source material), because a lot of these places are long-gone and/or very obscure. He makes a faint effort at combining entries when a town changed its name, but misses far more. What would you think of a town called Rust, which had a population of 375 in 1910, but thereafter disappeared? You won't learn here that in 1916 it changed its unpromising name to El Cerrito, under which it still flourishes today. Nor does he have anything to say about annexations or mergers, further undercutting the book's ostensible purpose, to enable readers to trace a place's population over time. I'm dismayed that this thing ever got published.
In trying to figure out where these places were, I wrestled on a library reference shelf with a huge volume titled California's Geographic Names by David L. Durham, which I also found on Wikipedia. This is a massive gazetteer of California place names, awesomely detailed, and, unlike Moffat, impeccably researched and thoroughly documented. Still, it has its weaknesses. Compiled by a geologist as a hobby over 30 years, it's great on topography, and thorough on such matters as whether a town had a post office, and when (often a surprisingly ephemeral distinction). But Durham is absolutely uninterested in governmental information or the needs of road map, instead of topographic map, users. He usually manages to say when a still-extant town was incorporated, but he says nothing of defunct incorporations or of annexations. He has an annoying habit of identifying the locations of non-municipality locales by listing the distance from the civic center of the nearest town, where the names of the streets at the main intersections would have been more useful. Nor is the nearest town necessarily the one that annexed the locale, if any did at all. Bayshore, for instance, the locale where the Cow Palace is (that's not mentioned either), is described as being N far north of SSF, and no mention is made that it's actually part of Daly City.
All this work, and they could have done a better job. Not a rare situation.