He lived in Paris (and Munich) in the first decade of the 20th century. In Paris, he continued his course of self-education by devoting his time to studying works in the museums and galleries. His paintings thereafter took on aspects of 19th-century French genre and landscape painting, a style suited to Jonnevold's representational approach to landscape. He was primarily a painter of the California landscape, with special emphasis on marine subjects (waves breaking on a rocky shore) and mountain vistas.
Sketchy at best, here's what SullivanGoss.com of Santa Barbara, CA says about years after Jonnevold's painting career. "Unfortunately, with the Great Depression, Jonnevold’s lack of funds lead him to a dispute with his landlord. After this incident he moved out of San Francisco, and disappeared from the art community."
TrotterGalleries.com of Carmel, CA adds, " Although he nearly lived to be 100, nearly 30 years after his disappearance, Jonnevold was thought only to have created works up to his seventies. His works have gained renewed respect in recent years and are highly sought after by collectors.
Sources: AskArt; Artists in California 1786 - 1940, Edan Milton Hughes, 3d ed.