While researching a plum variety I happened to find this Online Books Page (seems to be affiliated with University of Pennsylvania) with links to a large number of online books on plums. Many of these are public domain documents from state experiment stations (for example Iowa, Kansas, Texas, and Minnesota) from around 1900. The information is outdated but observations from reputable sources are always somewhat useful. I found it really interesting to see the commentary on varieties at the time and on growing advice. The native plums were viewed fairly positively in some of the documents, so it is disappointing that many were lost to time, but it was interesting to read about regardless. Moreover, many varieties of European and Asian plums that are still around today are mentioned.
Browse subject: Plum – Varieties | The Online Books Page (upenn.edu)
Another way of getting to a similar list is to 1) search “online books page University of Pennsylvania” to find the website, 2) click Search our Listings, 3) search “plums” in the title section.