For decades, anthropologists have combed the mountainous landscape of south-west France and the Spanish Pyrenees in an attempt to piece together the history of the Basque diaspora. Now, researchers are completing the puzzle with the help of a treasure trove of arborglyphs; thousands of 19th- and 20th-century tree carvings elaborately etched on to the trunks of aspen trees in the United States.

Some are rallying political cries for Basque solidarity, others depict the sexual fantasies of a lonely farmer, and many are no different from the graffiti found on school desks, simply stating such things as "Joxe was here".

Researchers cataloguing the arborglyphs say the carvings provide a blueprint for Basque immigration patterns and expose the psyche of the solitary sheepherder caught up in the Gold Rush that swept across the western US in the 1850s.

"The trees are a wonderful window into the Basque immigrant's way of life from the turn of the century to today. They provide insight into a group that is largely inaccessible in any other way" John Bieter, executive director of the Cenarrusa Centre for Basque Studies at Boise State University in Idaho, told The Independent.