For decades, North Jersey historians, art experts and naturalists had been stumped. Geoff Welch helped determine that an 1846 painting labeled "Janetta Falls, Passaic County" was really Clinton Falls. Where was Janetta Falls, Passaic County? Was there a Janetta Falls in Passaic County? Art experts wanted to know because Jasper F. Cropsey, a celebrated Hudson River School artist, painted several waterfall scenes in 1846 and identified them as Janetta Falls. "It's been a mystery for decades," said Kenneth W. Maddox, art historian at the Newington-Cropsey Foundation, in Hastings-on-Hudson, N.Y. Finally, thanks in part to an old magazine article, a local...