GENERAL LEVALLE, Argentina—Pilots often stare in disbelief when they make their first flight over this hamlet on the verdant pampa. There, on the monotonous plain below, is a giant guitar landscaped out of cypress and eucalyptus trees. It is more than two-thirds of a mile long.

Behind the great guitar of the pampa, and its 7,000-odd trees, is a love story that took a tragic turn.

The green guitar is the handiwork of a farmer named Pedro Martin Ureta, who is now 70. He embedded the design into his farm many years ago, and maintains it to this day, as a tribute to his late wife, Graciela Yraizoz, who died in 1977 at the age of 25.

"It's incredible to see a design that was so carefully planned, so far below," says Gabriel Pindek, a commercial pilot for Argentina's Austral Lineas Aereas. "There's nothing else like it."

Born to a ranching family with deep roots here, Mr. Ureta was something of a bohemian as a young man. He traveled to Europe and hobnobbed with artists and revolutionaries. After coming home in the late 1960s, the then-28-year old became captivated by Ms. Yraizoz, who was just 17 and dazzlingly pretty.