On the shoreline of San Leandro Bay, one particular work has caught the public eye and imagination for more than 35 years. Though the East Bay is a Sistine Chapel of graffiti, this particularly intriguing semi-circular slab of concrete brightens the day of many a passerby on their way to Oakland airport.

Watermelon Rock, a human-made landmark at the Martin Luther King Regional Shoreline Park, was originally painted as an orange slice in May 1983 by local resident Sandra Gibson and a friend. A few years later, someone repainted the rock as a slice of watermelon.

Irritated residents thought the painted rock ruined the natural look of the shoreline. One particularly angry resident painted it black, though it was quickly restored to its fruity facade.

The mystery of Watermelon Rock is that no one knows who re-paints it or why—rumors of the artists’ identities range from mermaids to a local college sports team. Through the years, it has had stints as a lemon wedge and other citrus slices, but it always returns to its beloved look as a watermelon.

The perfectly-shaped piece of concrete was added to the shoreline to bolster it after World War II. Sometimes, as the tide rises and falls in the channel, the watermelon is submerged by the water, only to appear again soon after.