Elm stump

I'm assuming these are considered to be petrified variations of the listed trees. It seems odd to do that since the names are very recent compared to the length of time to become petrified.

Yeah, the sedimentary unit hosting the fossil stumps is very young by geologic standards, mid-Miocene, say 15 million years or so, so the species are either still extant or at least closely related forms (like the gingko itself) still exist. Still, it's plenty of time for fossilization to occur. (Btw, "petrified" wood is archaic amongst paleontoogists; they just speak of "fossil" wood.) The occurrence is in a sedimentary unit intercalated between a couple of the Columbia River Basalt flows. For comparison, it's less than a quarter the age of the dinosaur extinction event, at about 65 million years ago. And the age of the famous Petrified Forest in Arizona is more ike 220 million years.

My only other visits to petrified (fossilized?) have been to the state park near Escalante, Utah and once to Petrified forest in AZ. I don't recall in either of those the use of contemporary names, but I see now the link. Maybe they used the scientific names in those other parks, which somehow makes it seem less contemporary. "Elm" has so many uses in literature that its hard not to link the word to 19th and 20th century American literature.