This is particularly noticable along the Pony Express Trail in the desolate areas of the west. Everywhere there is water there is a big patch of currants or chokecherries
More recent but one can see lots of daffodils around old homestead sites in various places in the Willamette Valley. Also old apple trees in the middle of nowhere .
Much of the Pacific Northwest (coast, including lake coast) is extremely rocky with scant amounts of sand. Much of it, heavily wooded, even today. A number of invasive species (like the Himalayan Blackberry) have muddled sites, that would have been obvious, based solely on plant sign.