There are a variety of clues which may suggest that Vikings penetrated further south and west into North America than (as has been confirmed) Newfoundland. Some of these are faint possibilities, such as an expedition which may have lain behind the Kensington Runestone, which was discovered in Minnesota in 1898. While highly skeptical regarding this artifact, we may keep open to the very slight possibility of its authenticity. This is even more true regarding the Yarmouth Stone and the Narragansett Runestone, discovered in Nova Scotia and Rhode Island in 1812 and 1984, respectively. Their locations make them more likely to be authentic than Kensington, although they are not without their problems, some of which are serious. When it comes to the Maine Penny, said to have been discovered in Maine in 1957, we are on much surer ground, even if its routeway to its eventual find-spot was probably via Native American trade networks rather than any direct Norse presence at the site.
But there are also many cases of clear forgeries and hoaxes—or, possibly, Native American monuments which have been culturally hijacked in the search for evidence of Vikings. They mark an acceleration point in the history of the search for American Vikings which takes us beyond a search for historic penetration of the continent and instead reveals penetration of the minds and imaginations of later Americans. This was prompted by three main factors.
The first was increasing awareness of the saga claims (based on medieval Icelandic stories mixing traditions and legends) regarding exploration of North America—awareness which accelerated during the 19th century and continued through the 20th century to today. While there had been knowledge of them in Scandinavia and Iceland for centuries, this increased in North America after 1800 and particularly after 1850. Heightened awareness led to a search for corroborative evidence which was connected to the events narrated in the sagas.
The second was the increasing presence of Scandinavian pioneers and settlers in the western expansion of the United States in the 19th century. Some pioneers sought validation of their ownership of the newly taken land through references to ancient saga claims. By no means were all of these Scandinavian, but latter-day Norse played a major part in this process. For the most skeptical 21st-century commentators, the Kensington Runestone is an example of this process at work in the Midwest in the second half of the 19th century.